Well, Windows 2000 is actually NT 5 and a natural progression from NT 4. Some techs might prefer it for that reason, as it is more familiar to them.

XP is a perfectly good Windows OS, and is more modern.

If you are having to work with old hardware you might prefer Windows 2000 as it is less demanding on resources than XP.

Some businesses may be aiming to go straight to Vista, leaving out XP altogether?