The reason they will keep the same old FPS and RPG or any popular genre of game coming year by year is because they sell.
If you think about it like this, every year there is another "wave" of newcomers who will buy the newest COD or Final fantasy, simply because they will not have played the plder ones but want to get into the series after hearing of their popularity. You guys are thinking from a personal perspective of how things are being released and moved on(or not moved on from your point of view).. a kid seeing MW3 on an advert coming up to christmas may want it for christmas, even though they havn't played any COD games before, and so will another 250,000 other kids... or maybe another million kids for that matter.
An easier way of explaining this is the sport games, FIFA, Tiger Woods etc... they are more less the same crap every year with minor updates. So if you are into buying the new game yearly. then it sucks. But remember someone may not have bought a FIFA or TW game before and want to get into them, so the updated version at that time does stand significant, and sells regardless(maybe drawing in half a million new comers, who knows). Remember we aren't the only bunch of gamers in the world that developers make them for, they know that new waves of people come, and they lean towards these buyers also to help future sales. And if that's what it takes to keep them companies afloat, is that a bad thing?
Even another way of making this point stronger is to mention people who want updated re-releases of popular old skool games NOW.... because that is a very greedy way to think, as you are only wanting it for yourselves. Why not let other further generations enjoy the original games first too, then maybe an even prolonged future re-release will come 20 or 30 years down the line and with 10 better graphics and gameplay depending on the modern game mechanics and styles they have then... so why should a developer "waste" that re-release on YOU/US when they can save it for a much larger audience with a much better more improved later future release.
Whats not to say once a re-release comes out(lets say FF7) is being released on PS3 at Christmas this year, so people will play and enjoy it and it was a great success of a re-release. But then what happens in maybe 20yrs time is they want another re-release of the original but with the "even more modernised" RPG elements of the time.. re-releases should only be allowed after 20yrs prior to the original.. it is only these self centered people who moan and complain they want a modernised re-release.