But who's to say what one's ability is? Why not devote ALL your processing power to mining? Why not spend ALL of your money (except for what you require for the barest of necessities) to build more mining rigs? In other words, contribution never comes by one's "ability". People contribute what they are willing to contribute, every time. Not just in mining pools, but in all things.
It makes more sense, then, that the rules be "contribute what you are willing to contribute, and be compensated according to what others are willing to pay". Which is market exchange.
I was just commenting on the "it's not really exploitation". It probably is if you don't contribute what you can. I don't adress any of the other issues with this sort of pool.
But if you have 3 GPU and 1 P3 (all idle), and you contribute the P3, you're not contributing what you can. If the GPUs are used for folding@home, then you only have the P3 to contribute, and hence not exploiting.
I'm a market liberal kind of guy myself, so I don't think this kind of pool would work either unless it's a very tight group doing it. Like a family or similar.