As I've said elsewhere I fear that it's actually worse then a lack of economic incentives, even in a Communist utopia it won't work because knowledge can not be encoded through semantic predicates.
I mean, its clear that all knowledge probably can't (probably can't encode all knowledge in english either), but it seems intuitively obvious to me that there exists a useful subset of knowledge that can be, given sufficient effort. I think ability to encode useful knowledge in principle in semantic triples is about the only problem the semantic web doesn't have.
I've ranted about this before[1] and you can read it when searching for my nickname.
It is ultimately a philosophic question about the meaning of semantics (sorry), but suggest to a modern linguist that knowledge can be grounded with predicates logic and they'll tell you "Dude we haven't been trying to do this for more then a 100 years, ever since Wittgenstein had a nervous breakdown".
It is a shame the semantic web doesn't pay attention to other fields that have studied this questions, or maybe some did and left :)
"Semantics" is a very overloaded term, but i'm not sure the goal of the semantic web matches the goals of "semantics" in other fields that you are thinking of.