They obviously payed Bethesda as they do to every game review company. There is no other reason except xbox being the graphically easiest system to program because it is slightly behind the times ATM.
Xbox is easier than PS3 to program for because most game engines and dev tools are designed for one or more general-use processors and a GPU. It's not that the 360 is easier to program for so much as the PS3 is difficult to program for, just like the PS2 was. Sony always insists on using proprietary architectures. Sometimes their architectures are good, and sometimes the additional complexity seems a little pointless. I'm not going to say which one of those categories I think Cell falls into, but if Sony wanted their systems to be easy to develop for it's within their power to make it happen. They choose not to.
I'm a software developer myself...I've never developed anything for PS3, but I have two friends that have. They are not fans of developing things for Cell. I'm not saying the PS3 isn't a capable machine (outside of the GPU it's probably more capable than the 360), I'm saying it could be just as capable while being easier to develop for. Sorry, but that's Sony's fault. They need to start complying with standard practices rather than trying to dictate them at every turn. They do this in all of their product lines...not just game consoles.
That said, this has nothing to do with DLC. Game content is very likely close to the same on all versions of the game (outside of textures and such). The differences in programming are in the engine, not the content. DLC release dates should have nothing to do with programming difficulty.
Sick of getting screwed by the money beast that is MS,
Drew
So, it's MS's fault that Bethesda is selling DLC exclusivity? Right...I forgot about MS's voodoo mind control powers. Darn you and your powerful juju, MS!