MT started before some years with the Grid. Almost the same time Amazon's S3 and EC2 come up, starting for the on-demand web services, a new era.
And now Rackspace comes with an expensive way [Mosso, even they don't support file access via SSH] to try to compete with an other player: Joyenet which gives free hosting for Facebook applications developers. Personally, after my bad experience with MT's Grid I'm not convinced that except Amazon's services, all the others really works.