But Blizzard wants them to be under the same interface, the WARDROBE interface, and it makes perfect sense. It's not exactly difficult to use a teleport to get back into a city when you do get an upgrade...
It's a non-issue that people will just have to get over. And the Yak is not "crazy expensive", I say this as someone who had 200k at most pre-WoD yet purchased it in MoP.