This behavior is not correct since Windows .NET does not exist. Windows .NET was renamed to Windows 2003 before it was released. So $os should return 2003 instead of .NET
There sure is Ctrl+Break and it works but only until before (Not responding) is printed in the titlebar. After you see (Not responding), Ctrl+Break doesn't work. Note that I've only seen this on WinXP, I have no idea what happens on other Windows versions.