Bare aluminum will corrode quite quickly, forming that white powder mentioned previously. That powder, aluminum oxide, is very hard and abrasive. If even small amounts of that gets on the moving parts it could cause accelerated wear.
Another concern is surface corrosion can greatly lower the fatigue strength of the metal. My guess is that this light, small frame is operating at relatively high stress levels so this could be a concern.
I believe that you will find a bead blast finish on aluminum will show scratches and wear rather quickly as compared to bead blasted stainless steel.
Having said that, I love bead blast finishes.
Just my $.02.