I have to say, I do have a "wolverine" character...but he's a Halfling. 

Sort of. I think there's a good distinction to be made between "potent" and "gamebreaking." Character optimization is about system mastery, so a good optimizer is aiming towards "potent" at whatever it is that character does, using all sorts of interesting tools, working within the constraints of campaign setting and style.
Very true; sometime a setting's theme simply demand that certain things be excluded.While "everything" might have an appeal, it isn't always appropriate in a given campaign setting.If you're playing in a Dark Sun world, a Decanter of Endless Water is an inappropriate item. The spells needed to craft it aren't even supposed to exist in that setting.
It's your campaign, so I won't tell you that you're wrong for strictly adhering to Roman mythology. But given all the crazy races and monsters in classical mythology, anthro turtle people wouldn't exactly stick out.Our setting is the ancient Mediterranean world of the Roman Empire. Teenage Mutant Ninja Turtles (i.e. anthropomorphic Turtle people) aren't setting appropriate since there were no ancient world legends of such folk.
Is refluffing not an option? If a player thought that the PrC would really fit his cleric of Ares, you wouldn't let him just file the serial numbers off and slap on a new title? (Possibly with a couple of simple alignment-related tweaks, if Ares isn't Lawful and Evil in your game.)For example, a PRC like Fist of Hextor is only appropriate in a campaign that uses the D&D pantheons. If there no Hextor, how can anyone by a warrior/priest of Hextor?
Probably the delusion that 'Asking for forgiveness is easier than asking for permission.'I've never understood why more players don't simply say "I would like class/feat/item X. Is that acceptable?" rather than just showing up with it.
Don't know if this portion is directed at me, but yeah, this is exactly my point. Asking forgiveness arguably has an advantage in other situations, in which the action in question is irrevocable, like "Sorry I borrowed your porsche without asking dad. My boss offered me overtime to come into work today, and hey, I didn't put a ding on it!" Dad's more likely to forgive and forget, because the deed's been done and getting angry won't change it.As for the "forgiveness" v "permission" approach: Why would I accept an empty and insincere "sorry" more readily than I would accept a "May I please"? The "forgiveness" approach decides in advance to take what they want and try to get away with it, and as a philosophy it says that they'll take what they want next time as well. If they're already planning their next offense, they aren't really "sorry" about this one.