Just to play a little bit of devil's advocate, there are avenues for expanding powers in the DCAU, and in fact, there were a few examples here and there. The most obvious example was when the Flash tapped into the Speed Force. I'm not sure anybody stood a chance against him. Fortunately, the writers obviously put restrictions on that angle, making it improbable or impractical for Flash ever to try that tactic again.
Another example, sort of, was "Hearts and Minds" when GL seemed to lose his ability to use the ring properly. It's not quite the same when power goes down, just to go back up, but the point is he had to re-train and refocus to become effective again. Any GL easily could fall into the anime character mold of having to train to become better to beat enemies. I wouldn't necessarily want to see that happen over and over again, but it's something the DCAU could have referenced more often, even if the hints were slight. It's not asking too much for GL to be better at his job than he was in day 1, especially when you consider a lot of fans think that's appropriate for Batman, even to the point of claiming that Batman's growing "power" is a result of good character evolution.
Lastly, I'm going to bring up the All-Star Superman comic line. IMO, the stories blow away any recent Superman story, DCU and DCAU alike. To me, it's the way Superman should be handled by more writers. Anyway, for those not familiar, Superman came into very close proximity of the sun, and as a result became much more powerful. The catch? It turned out to be seemingly lethal, as many of his cells progressed into apoptosis (normal accelerated programmed cell death). It's an example of how to write a story with growing powers. You can give a lot more, you just have to know where you have to take back in order to restore some balance of power and conflict.
The poster who started this thread has since been banned, so we'll probably never know. 
