They basically released Guitar hero games so fast that it got old... First two were ok, but then... Meh by the third one it got old real quick.
The sales analysts are both correct, and incorrect. The FPS shooter genre is still going good because they get an equal flow of new gamers to leaving gamers in shooters.
What they forget to mention is you can't take how a GENRE functions and apply it to a FRANCHISE. Call of Duty takes its time in releasing games, but they've seriously gone downhill, and we all know how senseless violence turns out for games... Great short term sales but drives off the big spenders. I remember the 2nd call of duty, it was a great game where you actually felt a small sense of nationalistic pride while playing, but now that they are improvising instead of basing them off of events, the games are getting more and more ridiculous.
Call of Duty will fall, and it will not be a gracious decent because this is activision we're talking about here. They milk it for all its worth then throw it out... I suspect black ops was its biggest hit, and it will likely get about 3-4 more games out if even that before the consumers get bored
Course the thing about FPS shooters is that when one game series dies, you can litterally take everything about it and re-make it into a new game with a different storyline and different systems to make it feel original. Heck, if you look at the history of FPS games they are extremely similar aside from the occasional "stealth" mode or "weapons system." (and because I know someone will misquote me, let me verify that there are occasionally acceptions to this rule of thumb, so don't go into a bashing spree.)