Just because you can run High workloads on AWS GovCloud, doesn't mean that Cloud.gov can run High.
From their own front page:
> We’re a great fit when:
> - Your applications are Moderate impact level or lower
I stand corrected!
There are different levels at the infra/platform/application layer. cloud.gov is built on top of AWS IaaS (though the PaaS could also be deployed on other infra).