How about we run the numbers for you LanEVENT. Intel wants to maximize profits, and Intel knows it can rightfully charge more for the dual processors than single ones (even AMD charges more for same speed MPs). Back when the P3 was Intel's top processor, Intel went overboard. The P3 1GHz with 256 kB cache currenly is being sold for $143. The P3 Xeon 1GHz with 256 kB cahce currently is being sold for $425. Look at the enormous price difference for basically the same speed chip. Now double that for a dual processor computer and the P3 chips alone will save you $560. This enormous savings gave a huge incentive for motherboard manufacturers to make dual P3 motherboards and sell them instead of dual P3 Xeon motherboards. There was enough consumer demand that it was worthwhile for the motherboard manufactuers to do it. Intel lost out on its greater profit since customers just purchased P3s instead of the P3 Xeons.
Fast forward to today. The 2.2 GHz P4 with 512 kB cache sells for $241. Intel changed the Xeon pricing strategy completely. A 2.2 GHz P4 Xeon with 512 kB cache sells for $262. If a customer could purchase a dual P4 they would save a measly 2*$21 = $42 - definately not worth the risk of running processors that aren't tested or approved for dual use. Thus there is little to no customer demand for dual P4 motherboards. No demand and you see there have not been any working motherboards designed yet. Intel is still happy since they get their price premium for the Xeons - customers are happy since they aren't paying excessive prices anymore. I use Xeons everyday - I certainly wouldn't risk using unapproved P4s just to save $42. Why do you want to?
Note 1: All prices I listed were official Intel
prices in lots of 1000 chips - street prices can and do vary.
Note 2: It is rediculous to argue that a dual P4 motherboard will cost significantly less than a dual P4 Xeon motherboard - everything will be basically the same... So i stand pat with my $42 number.