It's not an exclusive arrangement since Best Buy says it will still continue to offer HD DVD. But having Best Buy's valuable endorsement in the form of Sunday circulars, front-and-center store kiosks, and staff recommendation seems to be the icing on the cake for a Blu-ray victory in the format war, and potentially the death rattle for HD DVD.
The HD DVD Promotional Group responded with a statement "We have long held the belief that HD DVD is the best format for consumers based on quality and value, and with more than 1 million HD DVD players on the market, it's unfortunate to see Netflix make the decision to only stock Blu-ray titles going forward. While the Best Buy announcement says they will recommend Blu-ray, at least they will continue to carry HD DVD and offer consumers a choice at retail."