BioWare actually is doing this to a degree already for SWTOR. They are giving out free 30 days of playtime if you have a character level 50 and/or (not sure the specifics) a legacy level of 6 by a certain date. Translation: You get rewarded for sticking with the game and playing a lot, which in turn populates the world and theoretically makes it more fun for others to play the game since it's populated.
IBM put so much waste into the water and soil in Poughkeepsie NY (on the Hudson) that it now has to keep buildings up, even if it has no actual staff in them. Each building has built into it soil detoxifiers to clean up the land they befouled.