As you have analyzed in detail, there is a disconnect.
Effectively, we have two ways to use the Hide skill. One is the way it is usually (sic) done - as part of another action. Another is Sniping, which has its own action requirement.
However, since the first option allows hiding as part of an attack (note: an unspecified, general, attack), it encompasses every instance in which we might want to use the Sniping option. Since the Sniping option has an additional action requirement, it is useless, eclipsed by the "usual" method of hiding.
To answer your specific question: Yes, should combatant A foolishly decide to use the Sniping option of the Hide skill, combatant B automatically sees them, as A does not have the actions required to hide.
I suggest resolving all situations involving sniping using the "usual" rule (the one you described in Example 2). The sniping rule is broken.
You know the position of a visible creature. It really doesn't matter what sound it makes.
If a creature is invisible, you aren't evem aware it is there, unless you make a great spot check and it's within 30'.
If it makes a sound, you get a listen check. On success, you know of it's presence, but can't see or target it. If you beat it by 20, you pinpoint the location (meaning you can target the correct square on the grid with an attack, but the target still has total concealment and can't be targeted by a spell that targets a creature, with the exception of Effect: Ray).
This is a case where the Rules Compendium does not bring in a rule from an expansion book to the skill description, rather simply from the special abilities description for invisibility.
The PH2 Feat just makes this check better; the listener need only beat the DC by 10 to pinpoint the location, and, in addition adds +5 to these specific Listen checks (versus an invisible opponent). There is no case for where you need to pinpoint the sound of a visible opponent (since you already can see it...). This is a great feat for this specific purpose, increasing the odds by 75% to pinpoint an invisible opponent.
What does pinpoint mean? If you heard an invisible opponent, but you don't know where it is, you can make a melee or ranged attack against it, or attack using a spell that affects an area, but you have to guess the square the target actually occupies, and even if you guess correctly, the attack is against total concealment; 50% miss chance. If you succeed on the Listen check (by either +10 with the feat and a +5 modifier or by +20), you know the correct location (the square on the battle grid) but the opponent still benefits from total concealment and cannot be targeted by spells that target a creature. Note: The KES feat adds the benefit of direction on beating it by 5. That is markedly better than "somewhere" without the feat :)
This was my general understanding long before the Rules Compendium, but I do like that the RC made this explicit (hidden <==> invisible <==> total concealment).
If I am following your example, the DC to hear someone talking at 10' is 0+1, or 1. To pinpoint that person (if they were invisible) would be DC+20 or 21, or DC+10 with the feat or 11. A +10 modifier would negate the roll to hear, know direction or pinpoint.
Best Answer
The very first line of the skill description reads (roughly translated, I don't own an english book)
So yes, if the moon was a living being actively trying to hide, you would get a huge negative modifier. As the moon is not actively hiding, because it's just a mass of rock, you don't have to roll spot at all.
That said, somebody the size of a moon would probably grant a huge positive modifier, even if it were actively hiding.
Hide modifiers are:
The scale ends there, with colossal defined as 64 ft height or more. Given that the moon has the height of twice it's radius of 1737.10 km and a kilometer is 3280.84 feet, that would mean the moon would be 178098.34 categories above colossal. So if it actually did come to live and decide to actively hide in the clouds, he'd indeed stand a good chance not being spotted from earth.