I have never seen a camera manufacturer explicitly say not to clean a camera except by taking it to one of their shops. A better analogy is the car paint. The difference is that the paint on a car, if not washed carefully is more likely to be damaged and is much more difficult and expensive to replace. But people think they are competent with the tools even though the surface is a lot softer and damage prone than the AA filter made of lithium niobate which has a hardness in the 5.5 Mohs range, much more difficult to scratch than car paint. That is about the same as quality window glass, which is scratched by not many materials. Last time I checked few people have called the factory names for allowing their windows to be defective by needing to be cleaned. I even occasionally wash my own windows and have yet to damage one. Nor have I heard of there being a rash of people sending their windows to the factory for official cleaning.
So, since Nikon does not mention that cleaning is not permitted, and camera and lens cleaning has been a traditional photographer's task in maintaining his equipment, I am still trying to figure out who came up with the notion, just recently, that cleaning and dust as a defect that needed to be addressed by repair techs. It is a new claim that I have only run into on some forums in the last couple years. It is a pretty bizarre notion on the face of it. Stan St Petersburg Russia