1. Publishers usually send them the 360 versions.
2. The differences are almost always negligible and there are many other sites that do in-depth comparsions already, like Digital Foundry and Lens of Truth.
3. The guys have stated many times in the past that they prefer gaming on the 360. They are all achievements whores too so....
No they aren't. Not even Jeff chases achievements much anymore, and as far as I know Brad and Vinny never cared about them.
And their console preference has nothing to do with what version they record video of, unless they don't get a copy of the game and have to buy one.