That may be part of it. The flight sim skins are probably rarely seen outside of the simulators themselves or sites that cater to them. There's not much derogatory you could do to an airline there except crash their plane. The carriers may see it as a net positive or at least not a big negative Depends on the company and the circumstances. If you were to do something using their livery that the airline didn't like, it would probably be a different story.

There was a piece on the news the other night about a woman who had gotten a micro finance loan and opened up a small party store that sells balloons, pinatas etc. She had Disney characters all over the place. Given how touchy Disney is about their stuff, I wondered if she would be getting a call from their lawyers - assuming the characters weren't licensed. 

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken