Originally Posted by Jester FPS
Because the cpu is distributing the workload. You're not priming right if you're doing it this way, get sp2004 and make sure you open up two instances and set CPU: 0 and CPU: 1 in each opened application. Make sure "No Affinity" is unchecked. Then look at each cpu, they should be at 100% utilization each.
I'm not sure what you consider an optimized game, but the way dual core works is distributed workload. So in any single application, it's common that both core's are only utilizing 50% processing power.