This won't mean much in the actual UI (though it may change where your mount is saved -- I haven't picked up a vehicle mount yet, so I'm not sure if they appear on the mounts screen or not), but what it does mean is that Blizzard is stepping back from the vehicle interface. It's been buggy from the beginning, since beta and even after release, and while it's unlikely Blizzard will remove vehicles from the game, at least for the mount/vehicles, they're planning to go with the old mount code rather than have everyone using the vehicle code for that.
Interesting change. Hopefully Blizzard is also still working on tightening up the vehicle code -- it's never fun to jump into a siege tank and then discover that none of the abilities work. But for these mounts at least, they're backing off and going back to the old way.
Patch 3.1 brings us Ulduar, dual specs, significant changes to all the classes, and more! We've got you covered from top to bottom with our Guide to Patch 3.1.