Fair point! I'll try to answer with a question: So why is it that Google, Microsoft & Yahoo cooperate on schema.org to establish shared vocabulary?

They don't have to make it interoperable per se. It'd be enough to use some terms from a shared vocabulary (user, account, address) and then have some business-specific terms.

This way the business can use an existing library that knows how to handle user profiles. It's not that the full client has to be generic, a UI component that knows how to present a portion of a dictionary is enough.