Everything fell apart in late 2004.Why ? Because of lack of progress with IPF's top frequency.
BS! It is really quite simple, GFLOPs per dollar. Cheap clusters of 2s nodes have taken the HPC world by storm and the choice of processor is determined by GFLOP/ dollar with TDP an important second criterion.
At the prices Intel wants to sell IPF MPUs for even 3 GHz IPF chips would still be far behind Xeon and Opteron in GFLOPs per dollar.
Tukwila will be an amazing performer for HPC but it will still lose to x86 in GFLOPs/dollar which is more important to most HPC customers than absolute performance per node.