It appears the "Games on Demand" section has replaced "Xbox Originals" on Xbox.com marketplace. We're not exactly sure if this is a rebranding of Xbox Originals, but the title of the section would imply that all downloadable games -- which will include Xbox 360 titles in August -- will reside in this section. However, if you click on the "Xbox 360 Games" on the left navigation bar, there's a clearly marked "Full Game" download section, which is currently empty. Also, Xbox Live Arcade titles have a separate section as well.
Perhaps the downloadable Xbox 360 games will reside in two locations on Xbox.com? We've contacted Microsoft for clarification and we'll update as soon as we hear back.
Update: We're aware the Xbox Originals program has come to an end, we're just caught off guard by the lack of an official statement accompanying the change on Xbox.com (especially with no change on the 360 itself).