i work at an EB Games, and i'll use this simple arguement.
we've barely sold any copies of mirror's edge since it launched. we've sold more copies of the new 50 cent game which came out only a couple weeks ago.
more people bought Gears of War 2, while Uncharted barely moves.
i'm not saying any of these games are better than another. i really enjoyed gears of war 2, but uncharted was a brilliant game, but because it was a new title that no one had heard of, people steered clear. Mirror's Edge was great, but people in my store avoided it like the plague just because you werent primarily shooting people.
personally, i try to move these kinds of titles while i'm working, because i want people to see how good they are, but no one will do it because they'de rather play Halo 3 or something. i'm not saying halo 3 is bad, its just not original, and thats what this is all about.
i think consumers are primarily to blame. companies that see these kinds of sales market towards that. what sort of originality can we expect from Call of Duty 6? not much i'm betting, but it will be the best selling game out when it launches, and activision knows this. but if no one bought the next CoD game, i bet we'de see them rethink the franchise a little.
the gaming industry is a business for developers/publishers. there in it to make money. so i cant say there to blame when there only trying to create games that people will buy, instead of pouring cash into something that will just sit on store shelves.