Microsoft gets a lot of repeat buyers because of modding their consoles for piracy and not being able to send them in when they RROD/E74. Plus last fall when Microsoft locked and perma-banned a lot of modded 360's for piracy when MW2 came out, a lot of those people just went and bought new ones.
Plus Microsoft are the masters of marketing this gen. The over-whelming majority of multi-console games only have their 360 versions advertised in TV and elsewhere, which blind-sides anyone who does not stay on top of gaming news to know which game is coming out for which system. Personally, I didn't even know Dragon Age: Origins was coming out for PS3 until after it came out when I saw it in a Wal-Mart.
Microsoft is not stupid. Their console is not the best console by any stretch, but their marketing of it keeps it selling so well. They've even been caught trolling forums to hype and promote it like when a MS employee with a Microsoft email address was caught trolling NeoGAF to promote Forza over GT5. Unethical? Yes. Generates huge sales and results? Yes. Guess which one MS cares about?
