Last week in the comment thread for OverAchiever: Achievements to do before it's too late, there were a few notes from readers who were worried that noncombat pet achievements were going to disappear in Mists of Pandaria. This shocked me, because I could have sworn I saw pet achievements flash across the screen during the spam I always get when I copy my main to a beta or PTR, and I hadn't been aware that these achievements were actually missing from the General category. I was also sure there would have been some pretty high-profile news about it if developers were planning to axe them. Especially with the introduction of Pet Battles, it seemed like a very strange time for Blizzard to get rid of related achievements.
Then again, these are also the people who put the Aldor Rise elevator and Warsong Gulch rep in the game, so we already know they're capable of real cruelty.
OverAchiever's pretty much pointless if I don't use it to investigate stuff that I could have warned readers about well in advance, and pets are serious business. So, another character copy onto the beta later, I have an answer for you about what's going on.