I meant HTTP but I have to admit it was not clear. What I had in my mind when I wrote that was there needs to be something that forces people to provide semantics of web pages. By which I mean HTTP is too liberal, allowing any kind of document including documents without semantic annotations to be transferred. Therefore I thought people would provide page semantics if HTTP required documents be annotated with semantics just like HTTP requires Content-Type be given.
Ah, I see, that makes sense. The protocol level does seem like a good way to enforce it. Though I do have to wonder if, had that enforcement been put in place, people would have moved away from HTTP and toward a different, looser protocol on top of TCP. Or maybe that wouldn't have been practical. It's interesting to think how early, seemingly low level decisions about protocol design can have a profound effect on how things develop down the road.