IIS is unique in the sense that the version that ships with an operating system is the only version available for that operating system. Windows 2000 Server got IIS 5, 2003 got IIS 6, 2008 got IIS 7 and 2008 R2 has 7.5.
Does it make sense to synonym the IIS version (or somehow make some other relationship) so that users that favorite windows-server-2008-r2 tag also see iis7.5 in their favorites?