Someone can provide you with a clickable link, as in for instance this submission, and you would never even know that the content you are accessing is supposed to be "protected".
http://username:password@members.example.com
I wouldn't say that means the account in question is unprotected.
Why is "browser-support" relevant? Your example is not supported in MSIE. I also thought it was removed from Chrome (in the name of "simplicity"), but I may be wrong.
A link with query-strings is guaranteed to work for everyone.
Microsoft's solution to the problem may not have been ideal, but at least that was the reasoning behind it.
Edit: And what do you see once you click post? Hacker news ironically proving Microsoft's point. It's a wonderful world we live in.