Outside of Japan, it's not necessarily the software that causes sales to increase when we are this far in the lifecycle. Actually when big games release they usually get big commercial marketing. That means if its exclusive (sometimes multiplat) that console is getting advertised as well every time that game is advertised. It's in the public eye and makes more people aware. Also it keeps the perception up that it is a popular console with much to play on it and steady releases.
So it's not necessary the games itself (outside of a small hardcore group that might buy it for one game) but the advertising it gives the console. Only in Japan where there are these massive loyal fanbases to certain properties will it really cause a boost. There even this far into the lifecycle it has noticeable boosts.
