Yeah, they have to do SOMETHING. The last car I bought I specifically instructed (2 or 3 times) not to wash the car. It was pretty filthy with nice black brake dust on the wheels. The salesman assured me they were not washing it. When they brought it out the car was still dirty but the wheels were "clean" (and swirled) and the tires had greasy kid stuff on them. But they didn't wash it!
If you factory order a car, you deserve to get it untouched by dealer wash hands. Make sure you talk to them during the build/delivery process so you have an idea when the car will be arriving so you can get your hands on it as soon as possible after delivery. This minimizes the chances they will do something to it or that it gets bird crap on it in the lot. The last ordered car I was involved with, I was able to easily talk the dealer out of the "prep", although they "lost" the second key (if they do this to you, I would report it to your insurance company, and perhaps the police, I should have). Their big argument about you taking the car with the plastic on and unwashed is that there might be shipping damage they can't see and once you take it off the lot, they are no longer responsible. So look it over very carefully before you sign off.