[RPG] the penalty for stealthing at normal speed

It’s very difficult to prove a negative, but I am reasonably confident that no rule in 3.5 or Pathfinder explicitly states that all armors of a given weight class slow you down by the same amount. In 3.5, at least, there were certainly a few super-heavy armors that reduced the speed by more than your typical heavy armor (Races of Stone had a couple of these).

So yes, every Medium or Heavy armor must somehow explicitly state its own speed reduction, even if the overwhelming majority of them have the same speed reduction. On the other hand, if a given case failed to do so, I’d just chalk that up to the designers not realizing there was no such general rule, since it usually is so consistent and armors which slow people more or less than others in their category are quite rare. It’s also worth keeping in mind that it is consistently weight category that we should consider, not sheer weight.

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.