All of the 'hand car wash' sites around here use high pressure jet washers to initially clean their customers cars and that includes the door mirrors.
I have two friends who have had their cars damaged by the pressure washers used. One had paint stripped off, OK the paint probably wasn't very good, but a mains pressure washer wouldn't have stripped the paint. The other problem was a door mirror glass knocked out of alignment.
I still use a mains pressure brush to do mine, which isn't very often, although the windows get cleaned every week.
Vic.