I'm with you, I wash my own. Something about someone washing someone else's bike implies they could care less about how good a job they do.
Washing gives me an excuse to get up close and personal with my bike, able to see a problem before it gets worse.
I hardly ever allow the dealer to touch my bike. And hell no, I would not allow them to wash it, they will scratch it, or drop it and it will be my fault.
Getting it washed at the dealer after being serviced is a plus for me. Sometimes im really lazy to clean my bike. I dont have 2-3 hours for a complete detail. Even a quick wash im still gonna take 2-3 hours cause since i already started, I might as well as finish the job. I see nothing wrong with that. They have techs that wash and prep the bikes before selling and what not.