UEFI is not strictly a requirement for a GPT > 2 GB boot drive but also the latest OS since 2010, which is Windows 8 and Linux 3, which can read and detect GPT formatted partitions.
Apparently the hard drive makers have extended the sector size from 512 bytes to 4K in order to extend the life of bootable MBR partitions beyond 2GB. A legacy BIOS can boot from one of these drives.
AMD Sempron 3300+ @ 2.2GHz Barton Sock A 512Kb L2
ASUS A7N8X-E Deluxe nForce 2 MB
Seagate 7200.10 7200 RPM 250GB IDE w/ 8MB Cache Perpendicular
EVGA Geforce 7800GS 256MB AGP 8X
BFGTech Ageia Physx 128MB PPU PCI
1GB (512MBx2) Crucial Ballistix DDR400 4-4-4 Dual Channel
nVidia Soundstorm Dolby Digital Coaxial
Sony CPD-E540 21" CRT Monitor 1600x1200 85Hz VSYNC Off
Windows XP SP3