@RHCP: Well, considering how abusable the leveling system in PTA is, I'd bet on the character development. You can literally gain dozens of levels in one battle via triple battling with only a fair bit more effort than a single battle. Just... nobody cares to do it for one reason or another.
It probably has something to do with the fact that having a level 100 pokemon is pretty godmoddy in and of itself. If Pokemon Special is any indication, even the 70s are a stretch without some special powers to augment their already impressive abilities. The games also seem to support this what with the 70s being champion rematch levels. Of course we never got a level reading on what happened when Red's pikachu was augmented with Yellow's incredibly powerful special abilities... I think that might have actually overshot straight past level 100 completely by anywhere between 20 to 60 levels depending on how exactly that mechanic works (Addition vs Multiplication), if that's even plausible. o_o' Of course, such a thing would come off as incredibly godmoddy if applied to an OC...
Thus, an RPer must know the limits of their characters and limit their levels as such. For instance, my 'average-above average' characters typically have limits in the 50s.
Up until recently, only my evil characters ever went above 70. Dardanette has performance enhancing powers but lacks the sheer skill to rise into the 80s and one of my other characters uses unorthodox, extremely effective (and abusive) training methods to reach the sky high 80s.
The only good aligned character I've ever made that reaches into the 70s only does so because she's both an exceptional trainer with a dramatic specialization in strategy and most of her pokemon were raised individually before being traded to her as gifts on small teams.
I'm rambling though.