Hmm, didn't even see that one. I chose the cheapest six core listed on their models page - didn't think to add the hex to a base model.
Still, $3183 for a single hex core seems expensive when one can find the i7 hex core, 9GB ram, 1GB video card, and a BD-ROM/lightscribe burner for $1849 (also from HP!):
The $3183 hex is still $500 cheaper than Apple's 3.33 quad.
It's expensive because you're paying for workstation chipsets and ECC memory.
Just a case of different markets and different marketing strategies for them. Web prices on Xeon based stuff don't mean they are the prices you have to pay to get those systems.
Unless they are Apples, of course....