Late response but I'll take a stab at explaining this one:
1) R6 is an established franchise on XBox, and not on PS so they've got that going for them
I suppose that's a factor, but apparently it's already sold many more copies than the original.
2) 360 is *the* console for FPS gamers. I thought everyone knew that by now...
There's no doubt Live and the 360 controller seem to give an edge for fps as they seem to do relatively better than other multi-platform games, I just thought rsv2 was way too much off the ratios even with those factors considered but it seems the original quoted 99k for ps3 was what was wrong as it was actually over 150k (corrected in the thread).