[AshamedCaptain]

Nah, it's still the same protocol: https://www.virtualbox.org/browser/vbox/trunk/src/VBox/Devic...

What they dropped is the older Chromium/VMGL-based protocol for 3D acceleration , in favor of VMware's solution (which has at least one working open-source guest-side linux driver); but nothing else (and as far as I can see nothing from that page, so it's not really outdated).

[Narishma]

Is that why 3d acceleration doesn't work anymore in recent versions of VirtualBox in Windows 2000 or Windows XP guests?

[AshamedCaptain]

Well, and because they decided not to support the new 3D acceleration method on pre-Vista guests' Additions.