The only fully open source implementation of EFI is based on coreboot. Coreboot + tiano core provides a full open source EFI.
No EFI-based BIOS can make that statement.
Coreboot can reduce the costs of the platform, because 1. no per-unit license 2. distributed support model (same model as Linux, Apache, etc. etc. etc.) 3. Demonstrated higher quality than closed-source BIOS --> lower support costs
There is also a real security issue with closed source BIOSes, particularly EFI. The question is simple: what's your computer doing? The answer is simple: with a proprietary, closed-source BIOS like EFI that reserves the right to continue running once you boot, you do not and can not and never will know. People are starting to figure this out, and it's worrying them.
EFI is part of the old model of closed, proprietary software. coreboot is part of the open future.
ron