Guess they do exist:
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Buffalo announces worlds first external Blu-ray player
by Chris Marshall on Jan 8, 2008 at 07:32 AM
The MediaStation Blu-ray HD DVD drive is the market’s first external Blu-ray and HD DVD player that allows you to read and write Blu-ray content, which means you can save HD content, and connect the device via USB to your computer and view the content. When you are not doing that it will work for regular playback of HD DVD content.