pureScale has been worked on for over 4 years now
Exadata V1 was likely not quite dreamed up yet when the work on pureScale was started - 4+ years ago - just as scotdb said.
It takes years to build this kind of technology into a product - even when you are borrowing the architecture from another platform.
Oracle RAC is yesterdays technology that was designed on a message passing architecture through sockets - using vast quantities of CPU horsepower to service the context switches and interrupts that such communication entails.
Oracle has gone out of their way to try to get vendors to get emerging technologies like InfiniBand fit into their crappy design by insisting on RDS - so that it looks and feels like sockets - so that they don't have to make the deep investment to exploit RDMA and IB in its native form through uDAPL or MPI - from usespace to userspace - no interrupts - no wasted memcpy into the kernel and system calls etc.
RDMA is here to stay and will be mainstream on 10G ethernet as well shortly. Oracle is behind the curve on this on.