Considering your statement, I agree. Extensions should depend on subordinate extensions of Xorg, not Xorg itself. If for some reason there's an extension that depends on a file in Xorg itself, perhaps that should be evaluated separately (and probably move the dependent file to a new/existing subordinate). Perhaps there was more discussion/thoughts than what I saw in that one post.
Off the top of my head, I'm not sure there are other extensions that may benefit. I'm not sure if a dependency on Xorg-lib.tcz where this extension would currently want Xorg-7.6-lib.tcz would work if say Xorg-7.7-lib.tcz was used to satisfy its dependency later.