[mindslight]

Sure, fans have become more energy optimized. That doesn't support the implication that the lightness was required to get the modern lower energy usage, nor that a better built (heavier) motor wouldn't be more efficient and last longer. That lack of longevity is what the "motor weighers" are lamenting - a major reason this whole topic is important is that we're currently unable to buy new more efficient appliances that will also last long.

> newer ones are brushless DC vs the single phase induction of old. I imagine newer fan design helps too.

Yes, this is the advance in drive circuitry that I referred to - same with the "DC motor" fans. It's still a fact that at the current consumer design point, adding more copper to the windings will increase weight, efficiency, and longevity.