I'm curious about what you make of Omeka, and whether you think it relates to OP's point. It's quite common in the digital humanities, but I've never seen it used outside that context.
I really like Omeka. It's a very cool project and we did look into it early on. Really though we chose WP because it's ubiquitous - no lock in, very powerful, easy for editors to use. With the right nudging it does all the things Omeka does.