So, you are saying that every time someone wants to test browser compatibility, the browser will prompt the user?
No, they're not doing that. Which means that the information is in the hands of anyone that cares. It just isn't in Apache server logs by default.
> And what's the adoption rate of those, I wonder... less than 1% of users?
About as high as the dynamic equivalent will be.
Which is why not replacing the useragent string is the only option that makes things better.