From what I've seen the potentiometers in electric guitars tend toward the large sizes, in the sense of physical dimensions, but I don't understand why that should be. For example, wouldn't it be beneficial to strat-like designs to be able to use smaller cavities?
Again from my experience, large pots tend to be rated 0.25W, while other panel mount sizes might be 0.1W. The current from a passive pickup is almost the definition of a small signal, so wouldn't it make sense to use lower power components?
Is there an electrical reason for sticking with heavier pots, or are there other considerations?