Well there are quite a few changes, to be fair. There just aren't any big ones aside from layering. Example is how macros work (and which macros work), a lot of interface based stuff, combat logging, various other minor things. The layering was meant to be the fix for big queues, the problem is that Blizzard announced like 2 servers, then in their infinite wisdom upped that to 4, and then slowly creeped out new ones on launch day while most servers still had queues that were large enough to fill multiple layers on multiple servers.
It's like they are scared of the inevitable drop off of players to the extent that they are allowing the launch to be a complete gridlock shitshow, they could have 3x as many servers.