and one more thing with large volume transaction processing is scaling out on I/O and ETL jobs.Oracle (and other DB vendors) offer a lot of utilities that scale out perfectly with least of development time.
For e.g. it would rather be a difficult deal to work with parsers to parse a Gigabit-data file with code we have to own up , than to use features these DBs directly offer to parallel-load into a ready to use table within minutes.