IIRC, Win2K would wait for most / all service startups to complete before showing the login prompt. XP and later would allow login to occur while many services were still starting up.

It's a tradeoff. A Win2K system was pretty responsive when you log in after a reboot/startup, but you've got to wait for that experience. In the days of spinning disks and single core CPUs, you had to fight those still-starting services for resources, making the first several minutes of XP usage painful.