Fascinating... monsters tend to have much more varied body types than humans do- there are quite a few that aren't even solid, and plenty more that aren't nearly as humanoid in shape as I am. I believe the assumption is that there's less of a difference because humans have to stick to what works with biology in order to survive, whereas a monster can make up the gaps with magic even if they wouldn't otherwise be able to function.

What makes tieflings in particular an exception to the template, do you know? Do they just happen to have tails, or are they notably more magical than other species?