Microsoft, according to rumours, designed the next box to use 8gigs of DDR3. Microsoft knew it would be too slow so they engineered this "move engine" to transfer data between the mobo faster and added 32megs of esram for high bandwidth. Essentially they crated the console to feed their 32megs of esram as fast as possible to make up for the lack of speed, like adding some N02 boosters to a honda civic so to speak. Whether this works out or not remains to be seen. Again, according to rumours, but that document detailing the move engine seems pretty legit.
Edit: Microsoft designed the console to try to give you GDDR5 speeds with trickeries, no idea if it'll work or not. If these rumours are true, MS can't make the changes in time for a release. They'd either have to delay the console a good year or more to make that change. They'll just stick with their guns.
