We always cropped our Great Danes' ears, and would do so with any dog we owned that traditionally was cropped. For me, it IS about aesthetics, but also about the heritage of the breeds. Additionally, as such dogs are cropped, breeders have spent little, if any, attention on the shape or proportion of the ear. Consequently, in the GD world, I see some dogs who look quite attractive with 'natural' ears, but many others who have 'Dumbo' ears that actually get in the way when the dog is active.
Whilst I agree that cropped dogs' ears seem to get dirty faster, the only dogs we've owned who developed ear infections (fungal) were our natural eared Irish Wolfhounds.
CeeCee, my view on this is the same as Cody's: cropping may interfere with communication, but only when the crop is extreme -- literally to the nub -- rendering the ear immobile. Our GDs had a full range of motion in theirs -- they could lay them back, turn them, prick them alertly, etc. In terms of the crop, itself, giving the wrong signals, as Cody said, there is an abundance of breeds with naturally standing ears. Hence I really don't think this is a problem for other dogs.