You are correct. I read the same in 08 CX-9 shop manual. The manual even doesn't want you to inspect it, not mention replacing the fluid. But I have to believe that these "maintenance free" parts just mean that they do not need maintenance *within* the warranty. After that? well, it's your problem not theirs. Anyways, I also recall someone saying that the shop manual for newer CX-9 actually shows how to replace transfer case fluid. I will post it here if I can find it.
I just purchased my CX-9 and have not looked into how to change transfer case fluid yet. I am interested in what you learn. If you are having trouble finding info, I will try to get mine on a lift and take pictures. There should be a drain plug and fill plug no matter what the manufacturer says.