You are technically right, I can't argue with that.
But as a different point of view, how many MP owners even need a Xeon vs the non-Xeon version? Maybe some scientific or medical researchers need that ECC ram support, but most MP owners seem to be either enthusiasts or in the media industry. Since most don't really need or want Xeon/ECC, we're really two generations behind what we'd like to have. I suspect most would rather have a more up to date processor and less expensive RAM.
Of course I know there are exceptions, which is why I say "most".
I grudgingly agree. The artists in our Art dept, and the Art director all pummel their Mac Pros with large HD video projects, quite a lot of which includes that 3D graphics flying around stuff like the opening of Colbert or Daily show. Huge render times. Heck even just designing the graphics apparently taxes them pretty hard. But the rest of our Marketing Mac users would be better served by Minis or iMacs.
I swear half of the market for Mac Pros is just the whole cachet of owning the most expensive Mac money can buy. Well that and there are of course old graphics folks that came up on the Mac IIFX, Quadra 950, Power Mac 9600, Graphite/Quicksilver/Mirror, Mac Pro.....Mac Pro. Some folks just have to see a big case on the floor.