It proves that they are developing functionality that I've been looking for and some I didn't even know I wanted.
It is evidence that they want to be a great tool for developers and that they recognize their tool needs work.
It proves that I made the right decision (completely subjective which is the nature of a comment like the one I made) in moving away from Google for a more user centered and open-source browser.
And yes it proves that they listen to their users.
All of that is assuming they weren't lying or creating fake mockups (which I feel is a safe bet). Sure that's not a lot of proof for a scientific theory, but for a decision on which browser I want to use and which company I want to support I think it's proof enough :-)