When you are a company as large as Amazon.com it makes sense that in the looming format war between HD and Blu-ray, the web portal would declare themselves agnostic.
According to Home Media Retailing, Amazon is utilizing "CustomFlix, the wholly owned video-on-demand arm for the leading online retailer," and they "will support high-definition content from multiple formats - Blu-ray, HD DVD and Windows Media Video High-Definition DVD (WMV-HD DVD)."
They are "able to offer multi-format support thanks to a proprietary storage and repurposing platform that is designed to allow deployment of digitized files in different formats."
CustomFlix also has content deals with NBC Universal, A&E Home Video, and PBS. They make their titles available as DVDs on Demand through Amazon.com.