You do realize SPE usage doesn't really prove anything. The PS3 has only one true core, and 7 SPE's. Now, that said, these games do not use much of the SPE because of the difficulty in programming for it. If they could, they would program the games to take advantage of all the potential power, but they can't.
Programming games for 2+ cores is hard enough, but programming for 1 real core and 7 fake ones is pretty darned complicated. Also, there has been no game "max out" the PS3 usage, so we can't really compare SPE usage of 10-20% when we don't know what 100% usage would be. Killzone 2 pushes it to 60% SPE usage, and after 60% it starts to stutter and lag badly, so I think it is safe to say that for the next few years, nothing will be able to use the PS3's processing advantage. Generally speaking video games will run perfectly fine off of a dual-core processor with 2.4GHz speed. The 360 3 core CPU with 3.2GHz is more than enough for any advanced game in terms of CPU power.
The only real advantage of the Cell is in physics and other advanced calculations.
