With all of the online video services now offering much of the same ( sometimes lousy ) content, the new differentiating factor seems to be high definition quality. Microsoft has been there for a while (with videos over Xbox Live), as has Apple (over the Apple TV), and now Amazon is joining the gang. The new HD option for Amazon Video On Demand is available starting today for some 500 movies and television shows. And the HD content will work with the set-top boxes Amazon streams to including the Roku and TiVo Series 3 devices. In addition, Amazon is launching On Demand on select Panasonic televisions today as well.