Your browser is too old to view our site. User agent problem?

Lately I have noticed more web sites that will block you if your browser is too old. Why not just give a warning and recommend a new browser. I had one PC with this problem and Internet Explorer 8. So I went to a few test pages like whatismybrowser.com and they show I am using IE6 compatibility mode. Compatibility mode is NOT on. If you have this problem, go to the registry and delete Pre and Post tokens. All the blocked sites work now.

HKEY_LOCAL_MACHINE (or HKEY_CURRENT_USER)
   SOFTWARE
      Microsoft
         Windows
            CurrentVersion
               Internet Settings
                  User Agent
                     Pre Platform
                        Token = Value
                     Post Platform
                        Token = Value