Not all campaign settings are the same. If, for example, you want to run a game set in George Martin's world, animals are pretty much it for "monsters" to fight, and we don't want to exclude that kind of game. Or for that matter, read some Conan stories. Conan was ALWAYS fighting animals (usually gorillas, it seemed), and those stories were great! Personally, I think that animals make for excellent foes—we certainly used them to good extent in Dungeon's "Savage Tide" adventure path. And there's always things like gladitorial fights where the PCs have to fight an enraged rhino or tiger. And they make for nice bits of "realistic" encounters in the wilderness.
Beyond that, it's important to have stats for them for druid characters, who are always either changing into animals or summoning them or getting companions and the like.
The concept of leaving all animals out of a monster book is as much of a crime as leaving out all demons, or all dragons, or all fey. Animals are a part of the game, after all!!
As for the spikeys... we did try VERY HARD to abandon that concept. In fact, we tried to more or less abandon the concept of "Dire Animals" as a category altogether. We couldn't TOTALLY abandon it, because we wanted to maintain the familiarity and compatibility with 3.5, but what we COULD do was take the dire animals out of a dire animal ghetto and treat them like normal monsters and let them and their normal animal friends be alphabetized like everything else. And then I kind of made it my own personal crusade to treat the dire animals as basically prehistoric versions of animals... that is, after all, where all this dire nonsense comes from. The dire wolf has been in the game forever because the real-world prehistoric wolf is called a "dire wolf." Applying the word "dire" to all sorts of other animals has always been a pet peeve of mine. Better to have a sabre-toothed tiger or smilodon than a "dire tiger" I think, or a cave bear or short-faced bear than a "dire bear." And so we seeded that concept in the book as well.
Getting back to those "back antlers," you'll note that the bear IS the only one in the book that kept that feature. We quite consciously and specifically made sure to NOT have things like that on our animal art because I agree... it's silly. I killed more than a few pieces of art in the book because they had "back antlers." The bear's illo made it through because it had the right combo of having back antlers that, comparatively, were pretty unobtrusive and minor (especially compared to the ones that originally graced some of the others, like the daeodon [dire boar]). Of course, now that he's the ONLY one in the book with the stuff, they look more obvious and blatant. I probably should have killed that art as well, but each piece of art we had to kill at that stage cost us money, so I was in a place where I was having to pick and choose my fights. We decided to let the bear illo go and fix some other problems (not necessarily dire-animal related) instead. And to be honest, the fact that the bear has bony shoulders annoys me less than the silly expression he has ("A surprise birthday party? for ME?) on his face.
