so wait...which machine is apple selling to HD video editors?
An iMac or MacBookPro won't do it because you need more hard drive throughput (RAID 0) than either of those can manage if you're dealing with a lot of content.
And yet a Mac Pro with 4 internal SATA drives and an external 8-port RAID controller can push/pull 300+ MB per second. If that Mac Pro had i7 processors in it, then the FinalCut Pro junkies would probably actually have faster render times, too. I am pretty sure that Apple sells a lot more Macs to FCP users than to xGrid users who honestly could care less which OS is running their custom-compiled simulations and molecular computations.
It seems like some combination of arrogance/laziness than is keeping them from releasing a machine that could truly sing with their own flagship editing suite at a reasonable price. An i7-based Mac Pro with an externally-powered RAID box could probably cut complex video task processing time down 20-30% and end up costing less. Apple could make one and add an extra 500 bucks premium over their current Mac Pro premium and it would STILL be cheaper just because the relatively exotic (expensive) RAM and CPU were mainstream.
The Core i7 900 series processors all have a matching Xeon 3000 series processor, the only real difference for most people being ECC memory support. Apple use the Xeon 3000 series in the single processor Mac Pro. Those used in the dual processor Mac Pro (5000 series) just have the ability to interact with another processor, they perform the same with the same specs, you just pay a premium to have two in one system. ECC memory is like $10/GB more than non-ECC so that matters little too in the pricing.
Basically there is no reason for Apple to sell a Core i7 Mac Pro.