This should just serve as a reminder for those who want this sort of thing and are dedicated raiders to try hard and often at achievements/hard mode in Ulduar from the get go.
Instead, it's just going to cause some of those same people to freak out until 3.1.
It's cool, I'm betting they will continue to offer 310% mounts for the 10/25 man PvE achievements from here on out. It's a nice little reward that isn't game breaking.