Jackinthegreen
Explorer
Wow. Now there are exceptions. You're not consistent, man.
The rules themselves are not consistent, and not everyone will agree on certain interpretations. Likewise, even if people can agree on what the rules say, it's quite possible that they also agree the RAW is entirely nonsensical and using them as such would make anyone look like a complete moron. The interpretation that a medium creature with innate 15 foot reach gets 30 foot reach, while potentially RAW, is absolutely absurd. Remember, the game cannot be played without judicious use of common sense (AKA house rules to some). This is a case of common sense because it's obvious the weapon is only big enough to grant an extra 5 feet of reach, and that the wielder's natural reach being different does not change that fact.
Likewise, there are no rules I've seen that specifically adjudicate what happens when a creature has a different reach from the standard based on its size. It is pretty much all implications such as a centaur only getting an additional 5 feet of reach because he only has a natural 5 foot reach to begin with. The fact that there don't seem to be any specific rules on the subject shows that it probably does need to be house ruled.
In short, there are times when the rules are RAWtarded and need to be changed for the game to work properly. One example is the lines where drowning puts a creature at 0 HP in the first round, regardless of HP, including negative HP. So you might have a Creature with Delay Death on it with negative infinity hit points, but dunk its head in some water and it immediately returns to exactly 0 HP. While the rules might allow this use, it is plainly broken and needs to be changed, if not by the company itself then by any reasonable DM or player.
I'll concede on what the rules say in one case: The Rules Compendium specifically say on page 151 that a creature using a reach weapon made for a creature of a smaller size category does not gain the weapon's reach. It's clear and concise. As with everything though, it is still up to those playing on whether to follow that to the letter, to change it a bit, or just toss the whole thing out.
A reason people not knowing of that rule would think a medium creature using a small reach weapon would get reach is that the small weapon grants the exact same reach as a medium version, thus the medium creature should get reach with it too.
Perhaps we can agree that the reach rules aren't sufficient enough to make a truly concrete argument either way about creatures with "abnormal reach" and that such a ruling needs to be left to participants in each game?