The problem lies with memory, or lack thereof. FB-DIMMs are running late and hot, but they work well when you can get enough. That is the problem, they can't get enough to launch at a level that Dell et al would find acceptable.
I beg to differ with Charlie on the blame aspect-- Intel chose FB-DIMM tech for the Dempsey chipset, and now they pay for it. How many quarters of "constrained" FB-DIMM availability will Intel be facing *after* they launch in May?