Good point. That's why no real life animals have horns.
No, that's why no real life humans give birth to goats and giraffes. Tieflings, on the other hand, are typically born to human mothers who are not designed to give birth to spawn with horns and tails. Also, the Tiefling's skull structure (that awful neanderthal brow-ridge) seems to indicate to me that they are born with horns intact. I can't see how growing the horns post-facto would allow for the skull to develop that way.
Good thing they're not reptiles, then.
By definition, they are not mammals because they do not give birth to live young. You could make them vaguely Avian with none of the necessary traits or make up some new Draconic category, but they still don't give birth to live young or nurse their young - ergo breasts are simply there to facilitate bad art.
Well, anime-style catgirls for one thing. I can't believe that 4E left out the anime-style catgirls. That would have drove sales to an entirely new level.
Well, there are PC stats for the Shifters in the Monster Manual, and they are actually pretty solid - just keep them away from the Yiff-Yiff crowd.
- Marty Lund