(My parents would be delighted if Word or Excel had a similar library of documents.)
Since the Word and Excel documents often have no such metadata, and the possible attributes are numberous, it's no wonder no `document library' got popular as of yet. The best you get -- the state of the art of desktop search -- is full-text-search with some semantic analysis, right?
A sort of document library could be just as good or better than the filesystem for managing documents, I don’t think that you have to end up with a leaky abstraction. (Browsing documents on Google Docs, for example, doesn’t feel wrong but you are not using a filesystem to access your documents, you are using a sort of library view.)
I think it’s kind of astonishing that no one has really tried to do just that. There are half-hearted attempts but one of the things about abstractions is that they have to be good to be successful. It’s certainly not easy but I think it’s possible.