Yes. Apposition of 2 nouns tends to convert the first to an adjective. 'The member nations of the UN... ", "the service station...", etc. They are common and enumerable.

I can't speak for other native speakers, but I'll say this much: "of" is a totally legitimate preposition when showing possession. Grammatically speaking, there should always be an apostrophe followed by an "s" when saying stuff like "pc desktop." It's simply incorrect to not use it. Think about it: two nouns. Together. What's the meaning? The correct way would be to say the "PC's desktop." You *CANNOT* omit the apostrophe "S" and call it correct. Not by general grammarian standards. You see it done very often, though. Still doesn't make it correct. So what you've done there was pick up a horrible native speaker's habit. And same goes for the shape of the wall. You can say the "wall's shape." MUST HAVE AN S! I emphasize this because as a not-a-native-speaker-but-on-the-native-speaker-level person, I, too, had to learn English and I have found myself making the same stupid mistakes. Be very careful. The take-away message is this: you can switch the two nouns around as long as you use apostrophe "S" to denote which one possesses what. We know that "shape," for example, is always possessed by the wall and not the way around. The same goes for other things. Use logic, that's all I've got to say.