The Ps3 is actually doing rather well. The number you want here is really the attach-rate, which is at 6.57 for the Ps3.
If you look at TheSource's stickied threads, these are the attach rates for Nintendo's machines (I don't have the data for any others).
Lifetime attach rates by shipments:
NES - 8.1 games/console
SNES - 7.7 games/console
N64 - 6.8 games/console
GC - 9.6 games/console
GBA - 4.65 games/console
DS - 5.24 games/console (still increasing)
We know that the original Xbox had a lower attach rate than the GC, so the original XB is at around 9, most likely. You could also go to this: http://www.scei.co.jp/corporate/data/bizdataps2soft_e.html and see that the Ps2 is looking at an attach rate of around 10.
Now, attach rates only grow over the course of the generation. I wouldn't be surprised if we saw the Ps3 and Wii at 10ish, and the X360 at 12ish.
All in all: The Ps3 owners look to be buying equally many games as the owners of any previous machine did - only being outdone by the X360 and perhaps the Ps2/GC.
