Kind of.... For simple, low communication jobs this is true. But when you start trying to find the eigenvectors of a large sparse matrix, communication becomes your bottleneck, at which point MPI on commodity clusters (those without a really fancy interconnect) "works", but not fast enough to be useful.
I don't think "really fancy interconnects" makes a cluster not commodity, since the original post in this thread is about supercomputer processors. You can put Infiniband in any system with a PCI-e 3.0 bus.
Communication would become a bottleneck regardless of whether you're using MPI or something else. The problem you're talking about has nothing to do with MPI; it is intrinsic to distributed computing itself.
What would you define as a "commodity cluster"? To me it's a 512-core vendor-specific blade server with special interfaces to get more bandwith at lower latency across longer links. But maybe i'm just an old fogey.
blades were never more than a marketing trick: the offer nothing that can't be achieved in a standard chassis. there were a few multi-chassis SMP/NUMA machines that had cache coherency over external interfaces, but that was neither commodity nor HPC.
Kind of.... For simple, low communication jobs this is true. But when you start trying to find the eigenvectors of a large sparse matrix, communication becomes your bottleneck, at which point MPI on commodity clusters (those without a really fancy interconnect) "works", but not fast enough to be useful.