Oracle is not just the DB though, they have a lot of applications across several industries, such as utilities, health care, etc. And, there is also Oracle E-Business suite, which is a big competitor to SAP in the financial management system space.

So, they have other sources of revenue as well, and can likely build a large revenue stream of subscription services for business applications. (i.e. running PeopleSoft, EBS, etc. in the cloud).

I think IBM is in the game next to Azure with BlueMix. I've heard some talks about how they plan to get in the ring with Amazon and if it is not only smoke and mirrors they might succeed.