Wow, that's a lot for outside of Vegas. The new Marriott on the old convention center grounds has 1175 rooms, which I thought was the biggest around. Omni Shoreham and Wardman Park Marriott have like 2000 between them, with another 1000 and change nearby at the Hinckley Hilton, but that involves going outside for a block or four.
Atrium people probably prefer the sterile indoor habitat at the Gaylord. Not that I'm bitter about the theft of The Awakening or anything.
Don't cry for the Gaylord. They are killing on big conventions, there's no hotel in DC nearly as big and able to handle the big crowds. 2000 rooms.