Since they had to redo the renderer for PS3, a coder found a way to use shaders to make the background look a lot better. And since the 360 has a unified shader architecture, it gets the fix for free.
Bad news for PS3 fans is because of the memory they physically aren't able to load all the DLC on the game, and there isn't a solution yet. So they may have to pick and choose because adding all of it causes a performance hit.
The new expansion looks awesome.
http://www.1up.com/do/minisite?cId=3145462