Why is a cloud model chosen instead of a compute cluster (like the Titan), running maybe GPGPU? Or to put it another way, what kind of workload is benefited by a cloud instead of a compute cluster?
Off the top of my head, I'm thinking that a system like this could simplify carving/sharing resources - elasticity seems to be a defining "cloud" characteristic. Also, adding an additional layer of abstraction could enable/simplify upgrade of the underlying infrastructure.