Usability is not up. Each web site has its own, custom, non-standard user interface. I could teach my mom to use the web circa '96. I cannot teach her to use it today. It's too damn complex.
Usability would be up if the browser knew more about what to expect. You can look at things like Readability. The browser ought to know more about the content, and be able to present it in a coherent, usable way. The server-side shouldn't dictate presentation.