360 Version will sell more because of the userbase, not the content. I personally could give two shakes of a lambs tail about "additional chapters." And MANY people I know almost NEVER touch the storyline to begin with, so I'm much more inclined to believe they won't be buying a version based on extra storyline. However I believe the target demograph and userbase will sell more on the 360.
From 0 to KICKASS in .stupid seconds.







