The "server OS" bit came from software assuming that Windows NT 5.2 would always be Server 2003, and it was an incorrect assumption. If they had instead read th

The "server OS" bit came from software assuming that Windows NT 5.2 would always be Server 2003, and it was an incorrect assumption. If they had instead read the ProductType key and based the SKU lockout on WinNT (home/workstation) or ServerNT (server, obviously), no such issue would have happened. Windows 2000 was always NT 5.0 in both professional and server, such software had to use ProductType instead. Likewise, Windows Vista and Server 2008 are both NT 6.0. XP/Server 2003 is the only time when it deviated, and some 3rd-parties didn't notice the proper way to distinguish between client and server; becoming even worse once XP x64 came out and was actually NT 5.2 (XP 32-bit was NT 5.1).