The previous owner of my class C installed little convex bubble mirrors on the side rear view mirrors, and they do an excellent job of showing what is in the blind spot (and also showing well where the side of the motorhome is in relation to the lane lines). I'm sure camera systems can also do a good job; but mirrors have their advantages, too, such as being about as reliable as any technology comes and not breaking the bank.
For that matter, there's no reason why one can't have both convex mirrors and a camera system.