While companies like Blockbuster have thrown their weight behind Blu-ray, Video Business has reported that most major retailers are still supporting both high-def formats. With more and more people buying Blu-ray and HD DVD players, retailers have also started to devote more floor space to high-def titles and promote them in their weekly circulars.
Retailers are going mainstream with their marketing and merchandising efforts for high-definition discs as the number of titles released across the HD DVD and Blu-ray Disc formats approaches 1,000.

Amazon.com, Best Buy, Trans World, Virgin Megastores and others are promoting both formats, unwilling to potentially snub a portion of their early adopter consumers.

“Our feeling is that we should continue to supply both until the customers tell us that we shouldn’t,” said Jim Litwak, president and chief operating officer at Trans World. “Blu-ray is outperforming HD DVD in stores, but the customer is still telling us they want HD DVD.”
While most retailers are deciding to support both high-def formats, I wouldn't be surprised if some eventually decided to sell only Blu-ray titles, at least in their stores. If you'd like to read more, the entire article can be found here.