Perhaps I misinterpreted the original COTS post. I took the intent to mean that the USAF would develop "games" to run on a cluster of stock PS3s (like folding@home), not a cluster of dev kits. My point was that the stock PS3 OS might not have all the features necessary to operate in an MPI-based cluster. I suppose your "game" might be able to provide this environment, but that could get quite expensive.
As for building a cluster of dev kits, it is not price competitive against IBM's QS22. I believe a QS22 blade is (was?) somewhere around $8-10k a piece (excluding chassis costs). However, the blade has TWO higher-end Cell processors with all 8 SPUs functional in each and the blade can be configured with up to 32GB of memory (compare that to the PS3s 256MB). I'm not sure how many SPUs are functional on the dev kit. Still, it has only a single lower-end Cell, right?
Thus, the only price competitive solution for a dev kit is to use it to develop software for a cluster of stock PS3s. Which again, might not be able to do all the things it must in an MPI-based cluster.