Because I know NT's mem mgt sucks more than a vacuum pump (and causes me to reboot every couple days at work), and W2K's definitely has its quirks.
I wouldn't consider using anything from MS as a server. Like you, I like multiple boxes instead of dual boot. I don't particularly care for MS OS a client, but I do like (and do need) a lot of software that's only available on it; that's even true for my brother, who is a big Linux fan (for example, he's using Eagle for PC board design since it's an affordable, decent Linux program).
Better DOS emulation could be a plus, too.
Tony