Afaik Exadata wasn't even originally meant for OLTP. Seems like another case of a high-latency analytics/warehousing system being marketed as a "distributed database". They're now claiming that they can get OLTP grade performance with SSDs on Exadata, but I don't buy it. The promotion of Exadata is ironic, given I remember one of their engineers claiming (on his personal weblog) about impossibility of OLTP on top of shared nothing not too long ago.

As for the high-latency analytics databases (Vertica, Greenplum et al), I don't see much market for them either. Their big advantage over Hadoop was claimed to be the ability of non-programmer analysts to use them (via SQL), but Hive (which now even has JDBC drivers for it, allowing it to work with existing OLAP tools) solves that problem as well.