Its interesting how noses are sometimes turned up when speaking of year round detailing in snow country. Where do you think the dirtiest cars are? Kinda like asking a bank robber why he robs banks (because...that's where the money is).
There are opportunities everywhere. We have these things called garages, both heated and air conditioned.
In fact, I know some shops that are so busy in November and December putting on coatings, and then spring cleaning... that they can afford to take a month vacation in Florida in the winter watching other guys working.