A lot of places we have stayed in Europe just have the duvet, no top sheet. My son actually does this because he hates making his bed, and it just makes things easier.
BUT, you have to launder the duvet cover just as often as you would a sheet, and it is a big pain for me to get the thing on and off of the comforter. So it would not be my preference (unless I struck it rich and could hire a maid to do it.)
