Correct, Windows 2000 was NT 4.0++. But it was in my experience more stable, and way more usable as a desktop system.
As much as I am loathe to write it, a big part of its success in my opinion is that Microsoft focused more on the core Intel architecture and dropped DEC Alpha support, which must have been a huge resource drain due to the shenanigans one must do when developing for Alpha.
Alpha fanbois' loss is everyone else's gain. And while XP took that focus to the next level by dropping even more architectures (PC '98 and some SGI kit), it didn't really have the same impact, at least not until SP2.
Of course, for many folk, the greatest draw of Win2K versus XP is the lack of the all intrusive activation ....