Completely agree, building your own is cheaper, gives more control, etc. But what is more: you do NOT lose the ability to use the cloud for added reliability: it is pretty cheap to have an EC2 instance standing by that you fail over to.

If you are very database heavy, and you want to be able to replicate that to the cloud in real time it does get expensive, but if you can tolerate a little downtime while the database gets synced up and the instances spin up that's cheap too.