One thing missing from this analysis is the networking cost. The EC2 instance comes with 14gb/sec of dedicated EBS bandwidth and 25gb/sec of network bandwidth. That implies a 40gb NIC, which will require a 40gb top of rack switch and enough cross-sectional bandwidth in the datacenter fabric to handle however many of these machines they plan for (at whatever oversubscription ratio, if any).

That's a pretty non-trivial amount of expense to setup a network with enough capacity to support a machine like this fi you want to do it yourself.