I think you might have that wrong. Here's from Nvidia's SLI FAQ:
Do you have dedicated hardware for NVIDIA SLI technology or is it just software?
Yes. NVIDIA GPUs combined with an SLI®-Certified motherboard (which ships with the proprietary NVIDIA SLI connector) are the necessary building blocks for the SLI platform...
Source:
http://www.geforce.com/hardware/technology/sli/faq#c3
Crossfire will work any pretty much any motherboard in any slot (it might not perform well, but it will work). SLI requires at least x8 lanes for each GPU AND an SLI-certified motherboard. I believe this is still the case for dual GPU cards, they stil require "the proprietary Nvidia SLI connector"
I'm not 100% sure that I'm...