The real problem is, as technology has gotten better, graphics have gotten better. As graphics have gotten better art teams have gone from few, to being bigger than the size of an entire AAA game studio was less than a decade ago.
To make expansive worlds in cutting edge 3D is very costly. But most AAA developers focus on graphics and the game play, because customers want cutting edge graphics. Well they want both cutting edge graphics and innovative gameply, but rarely do they ever get it these days. Its really one or the other because both cutting edge 3D, plus expansive world, plus innovative gameplay = really really expensive.
And by cutting edge I dont mean bleeding edge. AAA games on the 360 and PS3 take a shit ton of artists and man hours to create the artwork and that all equals $$$.
Better graphics = more artists = more and more money and its only going to get worse.