I fervently agree with Paulinda and Donray regarding doing one's own laundry whilst on a cruise, either river or ocean. Why on earth would one waste precious cruising (or drinking) time doing hand laundry, when a perfectly decent laundry service is available for a modest (compared to the total expense of the trip) fee?
Another consideration is that the notion of having laundry hanging about in the fairly small cabins of riverboats would make the whole experience seem a bit too "tenement" for my taste. Like many of the other posters on this thread, we travel with easy-care clothing, e.g. Ex Officio and Patagonia, which work very well for hand-washing. However, we choose to use ship/riverboat laundry services, as we don't want to fool with such on a cruise. At home, we are happily masters of the washer & dryer; but on a cruise, we leave such nuisances to the boat's laundry service.
C'mon, people, indulge yourselves just a little bit more! It's your holiday, after all.