I guess your parent referred to the fact that NT didn't start with 1, as your earlier statement sounded like »XP is actually version 5.1 so what's the nonsense with iteration 4?«.
True, the first release of NT was named 3.1 to match the current Windows version, but then minor updates count as iterations as well and therefore XP is the 5th iteration (we will all agree that 2000 to XP is a major step).
My point was that if you want to find number laws, you will find making a point around them is really, really silly.
Unless I am mistaken, the following features were not available in Windows 2000: GDI+, Clear Type, Remote Desktop, Windows Media Player, much better Internet support, USB 2.0, FireWire 800, etc.
The list is very long. XP is not a big service pack. It includes everything that was missing in 2000 to make it consumer-ready.
None of those things couldn't be added with a service pack, and several were. XP and 2000 are basically the same OS.
I have no idea what you mean by 'better internet support' so I can't say anything about that.
Remote desktop did exist in 2k, it was called Terminal Services. All XP did was bring a stripped down server to the client.
GDI+ is available as a patch for Windows 2000.
There was nothing preventing MS from releasing ClearType on 2k, they just didn't.
Media Player 9 was released on Windows 2000.
USB 2.0 and FireWire 400/800 are supported in Windows 2000, they're just device drivers. A little googling seems to indicate they were added in Service Pack 3 or 4.
XP wasn't like Vista where they changed the driver model or made changes to the authentication system with UAC. XP was just addons to 2000, holding back things like the firewall and the last patch to DirectX 9 were artificial limitations to make XP seem worth the upgrade.
