Humans are all unique so there will be differing views of semantics. It does exist in pockets but not to the schema or spec as imagined. For instance, hashtags and geolocation on tweets, categories/tags within wordpress blogs, the social graph within facebook and others. Small pockets of semantic culture within.
When implementation is left to a large population, there will be differentiation as that is our nature. The semantic web wanted it easy, it wanted the implementers to organize. Organizing it with all the differences is how it will have to be. Unless a system implements the standard for you and each author upon creation, there will be differences, deltas and no standard.
Probably the best semantic web / metadata system that has been built does do this and that one is at the NSA.
When implementation is left to a large population, there will be differentiation as that is our nature. The semantic web wanted it easy, it wanted the implementers to organize. Organizing it with all the differences is how it will have to be. Unless a system implements the standard for you and each author upon creation, there will be differences, deltas and no standard.
Probably the best semantic web / metadata system that has been built does do this and that one is at the NSA.