Oracle's database as a service will run on Oracle's hardware, in other words, Exadata, where they will enable Columnar Compression and thus, ensure your database will always have to run on Exadata, no matter if in their cloud or not. Have fun with maintenance costs once you are forced to drink that kool aid every year.
Exadata also uses software raid and no proactive sparing, leading to things like both of your software mirrors going poof at the same time, resulting in data loss. Ask Oracle, it's happened already.
The only bright side to this setup is not having to pay the bills to power and cool their furnaces they call racks.
Note the Oracle cloud only supports Java, meaning it's less a cloud and more just virtualized Oracle. Still can't get Xen working on Exalogic eh Larry? Try using standards based Infiiniband