You get one attack roll for each natural attack you possess, and you do not get any extra natural attack for high BAB (you still gain extra weapon attacks for high BAB if you are using a weapon)

In the case of the Oliphant exposed, because both the Gore and Stamp attacks are primary, you get all the three attacks at your full BAB, and no extra attack because of a high BAB. Assuming your size is Huge:

Melee gore +11 (2d8+5), 2 stamps +11 (2d6+5)

Bonus break down: +8 BAB +5 Str -2 size (because all the three attacks are of primary type, the -5 penalty to secondary attacks does not apply)

The confusion happens because the no BAB extra natural attacks is not clearly stated in the monster rules natural attacks entry, but it is specified in the combat chapter in the natural attacks entry under the Attack section as referenced in the question.

For a full explanation about BAB and natural attacks, first of all, the rule which states you get extra attacks as your Base Bonus Attack (BAB) rises is under common terms definition:

Base Attack Bonus (BAB): Each creature has a base attack bonus and it represents its skill in combat. As a character gains levels or Hit Dice, his base attack bonus improves. When a creature's base attack bonus reaches +6, +11, or +16, he receives an additional attack in combat when he takes a full-attack action (which is one type of full-round action—see Combat).

So by the BAB rule you get additional attacks when you reach certain BAB levels.

Let's check what the natural attacks rules say:

Natural Attacks: Most creatures possess one or more natural attacks (attacks made without a weapon). These attacks fall into one of two categories, primary and secondary attacks. Primary attacks are made using the creature's full base attack bonus and add the creature's full Strength bonus on damage rolls. Secondary attacks are made using the creature's base attack bonus –5 and add only 1/2 the creature's Strength bonus on damage rolls. [...]

Creatures with natural attacks and attacks made with weapons can use both as part of a full attack action (although often a creature must forgo one natural attack for each weapon clutched in that limb, be it a claw, tentacle, or slam). Such creatures attack with their weapons normally but treat all of their natural attacks as secondary attacks during that attack, regardless of the attack's original type.

So nowhere says natural attacks do not get extra attacks for high BAB, but it neither says they do, and it makes a clear difference between natural attacks and attacks made with weapons. So the intention seems clear that natural and weapon attacks are different things and work differently.

The confusion is cleared when you check the natural attacks entry of the Combat section:

You do not receive additional natural attacks for a high base attack bonus.

We can also infer this works like that from examples. In this case take a look to the Bear in Paizo Bestiary. At one side we have the Grizzly Bear (BAB +3) at the other the Dire Bear (BAB +7):

Bear, Grizzly: Melee 2 claws +7 (1d6+5 plus grab), bite +7 (1d6+5) Base Atk +3; CMB +9 (+13 grapple); CMD 20 (24 vs. trip)

Bear, Dire: Melee 2 claws +13 (1d6+7 plus grab), bite +13 (1d8+7) Base Atk +7; CMB +15 (+19 grapple); CMD 26 (30 vs. trip)

As you can see the Dire Bear has +7 BAB, which corresponds to an attack iteration of +7/+2, but if you look at the Dire Bear attacks, he has exactly the same number and type of attacks than Grizzly bears. Thus, it seems that Pathfinder developers intention is high BAB does not give you access to additional natural attacks, and that is something reserved to weapon attacks, unnarmed strikes and combat maneveurs.

Remember you need to take a full-attack action in order to perform all your natural attacks, and you still benefit from additional attacks if you are holding at least one weapon.

Addendum about natural attack bonuses

When performing multiple natural attacks, you have also to take into account the difference between primary and secondary attacks. So let's see when a natural attack is considered primary or secundary based on the universal monster rules:

Primary: You attack with full BAB and full Strength damage bonus. Are considered primary:

• Typical primary natural attacks: Bite, Claw, Gore, Slam, Sting, Talons
• Whatever attack if it is the only type of natural attack the creature has (be it single attack as a Tile Slap, or multiple as 2 Pincers)

Secondary: You attack with BAB -5 and half Strengh damage bonus. The multiattack feat reduces this penalty from -5 to -2. Are considered secondary:

• Typical secondary natural attacks: Hoof, Tentacle, Wing, Pincers, Tail Slap, Others...
• Whatever attack if it is used in combination with weapon attacks (including unarmed strikes).

You almost always need a Full-round Action to take multiple attacks

Natural Weapons are not an exception

As a standard action, you can use any of your natural weapons to make a single attack. You cannot make attacks with multiple natural weapons, not even paired weapons like claws. If a weapon is “secondary” (it will say so in its description), it makes the attack at −5 even if it’s your only attack.

As a full-round action, you may attack once with each weapon. Only one weapon or pair of weapons can be “primary;” even if you have more than one weapon or pair of weapons that claim to be “primary” in their description, you must pick one or one pair to be primary, and all others are secondary. Secondary natural weapon attacks are taken at a −5 penalty.

This means your attack routine with two claws (primary pair) and a tail attack (secondary) is +0/+0/−5 at BAB +0.

There are some (rare) ways to attack more than once as a standard action, and some of them are compatible with natural weapons. These will explicitly state this exception to the usual, however.

Natural Weapons and Manufactured Weapons use totally separate rules

Natural weapons never receive iterative attacks, and there are no cumulative −5 penalties, only a single −5 penalty applied to all secondary natural attacks. If you have the Multiattack feat, all secondary natural weapons attack at a −2 penalty instead of a −5 penalty.

None of the rules about manufactured weapon attacks (iteratives, two-weapon fighting, Flurry of Blows, etc.) apply to natural weapons.

Thus at BAB +20, that same pair of primary claws and secondary tail slap attacks at +20/+20/+15, or +20/+20/+18 with Multiattack. If you added a pair of secondary Tentacle attacks, that would be +20/+20/+15/+15/+15 without Multiattack, or +20/+20/+18/+18/+18 with.

Unless otherwise specified by the natural weapon, primary natural weapons add your Strength modifier to damage, while secondary natural weapons add half your Strength modifier to damage.

You can mix manufactured weapons and natural weapons.

When you do so, you gain all your normal manufactured-weapon attacks (including iteratives), plus any natural weapons you have, each as a secondary weapon, with the caveat that you cannot use any natural weapons that are being use to hold a manufactured weapon. I.e. if you hold your sword in one hand and attack with it, you cannot use the Claw attack from that hand. If you instead two-hand a Great Axe, then you cannot use either Claw attack.

When you do this, you can mix natural weapons with full-attacks that use the two-weapon fighting combat option or Flurry of Blows class feature.

Example: Longsword, pair of claws, and tail slap

Thus if you had a Longsword, a pair of Claws, and a Tail Slap, your attack routine would be +0/−5/−5 (sword, claw, tail) for BAB +0. Multiattack improves this to +0/−2/−2. At BAB +20, it’s instead +20/+15/+10/+5/+15/+15 (sword, sword, sword, sword, claw, tail) or +20/+15/+10/+5/+18/+18 if you have Multiattack.

Same character with dual kukris and the Two-Weapon Fighting feat

If you instead have the Two-Weapon Fighting feat, and use that option with a pair of light weapons (call it a pair of Kukris), you attack at −2/−2/−7 (kukri, kukri, tail), since both hands with Claws are being used to attack with Kukris, and the Tail is always secondary when used with manufactured weapons (hence −5; note that Two-Weapon Fighting does not penalize it, however). The Multiattack feat would reduce the penalty, so the tail would be at −2 (+3 attack for one out of three attacks is not a great use of a feat, but just for completion’s sake).

At BAB +15 and with the Improved and Greater Two-Weapon Fighting feats, you get +13/+13/+8/+8/+3/+3/+10 (left kukri, right kukri, left kukri (2nd), right kukri (2nd), left kukri (3rd), right kukri (3rd), tail).