Historically, multi-CPU motherboards were generally graded “server” (i.e. expensive). Now that multi-core is pretty much defacto, you’d expect to be seeing multi-cpu motherboards in the desktop/workstation grade.
But most dual-cpu motherboards seem to be labelled “server” still. The pricing is coming down, although still significantly higher than single CPU motherboards.
My hunch is that when desktop performance consumers spent $500 on a motherboard, $2000 on a pair of i7 extremes and $500-$1500 for sufficient cooling, they’d be kinda upset when they found performance to be about the same as a single CPU, possibly even slower in many cases.
Uncovering why would damage Intel/AMDs calm. Perhaps blow the lid on the shameful state of current-gen multicore CPUs. No lengthy explanation this time, lets just say that I view the “Core i” gen CPUs as an alpha/beta market test.