Did you take a poll amongst bettas to come to that conclusion?
Many fish have a fairly wide range of temp variance in the wild, and considering that most are kept at room temperature and do just fine, I think they do fine at room temperature. If we were honestly trying to simulate water temps then the fish that come from shallow pools should get the big temp swings that happen in certain climates.
It's no different than the pH thing, do you adjust your pH to match that of the betta's natural (yet long removed) homeland waters?
One other thing to think about with cold blooded animals is that higher temps = higher metabolism. Everything speeds up, including aging.
Either way, I've kept my betta in room temp which varies around the mid 70s and he is currently in the low 80s in a 125g tank, he seems happy either way, but it could just be me.