nVidia basically terminated some contracts or let them expire without renewing them.
BFG recently went out of business because nVidia decided to stop using BFG as a business partner, thus they would no longer get any more nVidia GPUs.
nVidia ended their business partnership with XFX. At least XFX was able to partner up with AMD to bring forth thier own line of Radeon cards back in 2009. XFX probably got into the PSU business (all built by Seasonic) to expand their product mix. I think they started selling motherboards back in late 2008 / early 2009.
This move by nVidia allows them to remove established direct competitors from the retail market. It adds to thier bottomline 'cause they will still sell GPUs in bulk to thier partners (they are competitors now as well), and video cards in bulk to Best Buy. nVidia will probably get better profit margins on an entire video card rather than just a video chip.
nVidia might undercut the competition by offering their own cards for slightly less money because their partners still have to buy the GPU from nVidia. With fewer business partners and nVidia selling directly to retail... who knows, nVidia might have negotiated higher bulk prices for their GPUs to thier remaining partners.