I think your theory of it overheating is possible. Expecially if you were going several hours straight... In a perfect world, you should take like a 5 minute break every half hour. Let your tool cool off, and also good for yourself too. Something along the lines of holding onto a vibrating tool is NOT good for some part of the nervous system. I have personally experianced a numb sensation after working for a while with tools.
But the full rpm is probably to let the fans try to cool off the motor as much as they can. If you are into cars, it's like rockcrawling, and needing extra fans because the truck is moving too slowly to have air pass over the radiator.
