I didn't make any claims about performance per $, just relative performance compared to VMs. I hate Oracle as much as anyone but the EXADATA is impressive hardware. It has lots of RAM and Infiniband networking. It can push query predicates to the storage controllers to reduce the data that had to be transferred.
It is impressive. But for the same cost you can get vastly better performance with Postgres and bigger hardware.
It does come with internal redundancy, but do you need that? Also the cluster nature of it can come with some surprises as compared to a single database.