I have been thinking of the same thing, my reason is partially age but also I have a health condition that is making it hard for me to do a lot of things. One of the big things that I HATE when camping is I carry a lot of camera gear and every night I have to move it from the truck to the camper and each day I have to move it back again. Well for most people this is not a lot of work for me it takes a lot out of me. With a class B I can leave it in the front as I have access to it from the back so if anyone tries to steal it I will know and I can get my camera cards out at night to download.
The reason I have not made the move is that I have a boy still at home and need 3 seats for day trips and I have not found a nice one at a good price with the 3 captains seats. Second reason is that most class B,C & A's have poor insulation and that would eliminate winter camping - some B's also do not have a furnace just a heat strip in the air unit and that does not do a lot in -30C.
edit - One thing that I did notice when looking at a number of Class B's was that getting out of the side door was difficult. Had to really bend down and it was difficult to get out and in easily.