Ultra high end OLTP system leveraging Oracle RAC. It's a very specific use case that goes beyond basic replication where you require ACID compliance, HA, multi master (in this case via shared disks and distributed locks), all atop an MVCC database. The MVCC implementation of Oracle does not require a VACUUM style operation which is another plus for a 24/7 environment.
I know of a couple financial services companies that have this type of setup though I've yet to find one that (IMHO) really justifies it. In all cases they've got boatloads of money to throw at a problem and the guys in charge of making the tech decisions don't mind having one of those boats sail off to Larry Ellison.
Other idea - "prestige". "We are using top end solutions, unlike the lowly startups, we are serious businessmen see."
Edit: From what I saw Hyperion FM got relatively better after the Oracle acquisition.
In my experience the opposite seems to be true. I have heard people describe Hyperion as "pretty good" prior to the acquisition (this was a while ago, before my time). Today, if I talk to anyone about it, sentiments range from negative to very negative.
Almost every Oracle acquisition has suffered the same fate.