This whole PNTR thing did not originate with Bush or Clinton. It goes way on back to the Kissinger era.
Basically what this whole thing is about is... Back in the 70's when trade started the US required annual reviews of China trade based on all kinds of stuff. They extended them a package, then told the Chinese 'we are going to review it every single year'.
With the thing now, the package has not changed. Not the one we gave them at least. The only thing we did is end those annual reviews. It did not change any of the framework at all as far as I know.
I think we did that because it is required for China's WTO entry. Why is WTO important? It is not that it will give China more access to the US, but it will give the US more access to China. Supposedly it will make trade more reciprocal. At least thats the theory.
Actually, we made PNTR dependent on China joining the WTO, not the other way around. But you've got the essentials right. However, Bush is the one who made it permaaent, i.e., not subject to annual review.