It's a pity the net is already littered with indications of a 'buggy' 360 version and a 'really buggy' PS3 version...
I really don't like it when poorly coded games sell well as it just sends the wrong message to publishers... still, with the first release seeming pretty solid I guess people were entitled to expect an equally solid follow up.
I would imagine Resistance is getting a bump from newer PS3 owners who want to play it before the second one hits. If previews for RFOM2 are very good then I'd expect to see RFOM gain a nice halo effect in the run up to RFOM2's release.
Try to be reasonable... its easier than you think...