I never thought for a moment you were BSing me! It sounds like what you're talking about is the motor quality that erocker mentioned, below. Yup, a high torque motor will help to keep the fan speed up all right against resistance, without adding more voltage and is another important quality metric. I'd forgotten about it, so shoot me. Indeed, as to sneeky above. I never said there was any marketing gimmick here? And the dimples etc are the differences I'm talking about when comparing the quality of fans. The better fan will move the air faster at a certain revs than the poorer one and push back harder against air resistance in front of it, maintaining its speed better.