Any reason why it comes out on the 360 first?
its good for Bethesda in the long run considering how much they are paid to actually do this, also good for the other consoles as well some of the more serious bugs might be ironed out thanks to the xbox running into them first
Pretty much all this, plus Microsoft also gets to advertise X-Box 360 and Kinect alongside all advertisemants for the DLC, which in turn gets people motivated to purchase the console, the accessory, and the game. It's not necessarily a bad thing, since like §kyrim says, it also lets the more serious bugs get ironed out prior to release on other platforms, which benefits everyone there as well, so it's more or less a win-win situation. The only downfall to it being 30 days though, coupled with a beta, is that every spoiler about the DLC will flood out onto the internet, but there's ways to avoid coming across spoilers. Just try to avoid going onto the forums for awhile until the DLC releases if you're worried about spoilers.
Also, keep in mind that companies like Bethesda and Microsoft need money for the continued development of such things as more video games, as development costs aren't exactly getting any lower, so don't take anything I said as being against the idea of timed exclusives.