This is one of the sweetest things I've seen in WoW in a while. Love little details such as this that the developers take time and care to implement. :)
I wonder what happened to Hornsley, from the old version of the Darkmoon Faire, though. Hope he was released back into the wild to rejoin his thunder lizard kind.
Edit: Apparently Hornsley grew up! His pen is currently occupied by Crush, though, so maybe they rotate in and out of that particular pen.
Also, thanks to a tip from this Petopia forum thread, be sure to /hug one of the Pygmy Cockatrice critters wandering around the petting zoo area. ;)