SLI and crossfire require BIOS support, SLI has a licensing fee so not all boards that could support it do, crossfire is free so any board that can does. To get your board to support SLI you would have to get a modded BIOS but that voids you warranty and runs the possibility of bricking your board.
Actually you are only in part right. There is a little known hack that is floating around the net. I gave it a try and it worked with out issue.