Now I'm the one not reading. Sorry about that, I totally missed what you meant and yeah, you're totally right on that. People do keep buying crap. But if a company keeps ripping people off people will stop buying it. Madden didn't innovate and people stopped buying them. Yeah, they're made, but they're no longer a huge hit because people realized that they didn't need the new versions every single year.
CoD won't quite hit that, because the new versions actually offer something new. That "new" may just be new maps, but it's enough to get the bulk of the community to shift, and most people play the games not because of the games themselves but because of how large and competitive the multiplayer community is.