A big attraction to new users is that anyone with a computer can generate some free coins. When there are 5000 users, that incentive may fade, but for now it’s still true.
GPUs would prematurely limit the incentive to only those with high end GPU hardware. It’s inevitable that GPU compute clusters will eventually hog all the generated coins, but I don’t want to hasten that day. If the difficulty gets really high, that increases the value of each coin in a way since the supply becomes more limited. The supply is the same: 50 coins every 10 minutes.
But GPUs are much less evenly distributed, so the generated coins only go towards rewarding 20% of the people for joining the network instead of 100%.
I don’t mean to sound like a socialist, I don’t care if wealth is concentrated, but for now, we get more growth by giving that money to 100% of the people than giving it to 20%. Also, the longer we can delay the GPU arms race, the more mature the OpenCL libraries get, and the more people will have OpenCL compatible video cards. If we see from the difficulty factor that someone is using too much GPU, we can certainly pick this OpenCL stuff up again then. Maybe my effort to maintain GPU innocence is running out of time. It’s worked out so far.
Satoshi