Yeah but who knew that when they bought MGS3? I know people who still thoughti twas Solid Snake in the game.

I'm not disagreeing with your point. Sales going down after MGS2 is more of what you said for XIII because people were disappointed by both games and thus didn't care about the next installment.

Also I would think ME3 has the most sales of the trilogy since it's coming off 2, the absolute best ME game.