That is true, but what appfog (and the other PaaS providers) do not give is the ability to tweak service[1] configs even to a limited degree. Not needing to worry about Mongo or MySql setup is great, but for all of my non trivial use cases, I have had to adjust configs at least a little.

[1] Cloud Foundry(and by implication AppFog) differentiate apps from services, where services are backend infra like databases.