I can't quite agree with you on the price honestly. I don't think people actually compare similar computers when doing this sort of comparison on the Mac Pro, since it is rather high end with Xeon processors.
A quick compare of Dell T7500 workstation dual 2.26: $2,843 and Mac Pro dual 2.26 @ MacMall: $3,096.99.
The case alone would probably make a $100 difference, going from plastic to aluminum. Don't get me wrong, I think there's definitely a Mac Tax but that's the choice you make when purchasing the computer.
I chose Dell, just because the website is easy to quickly configure a similar computer, but I'm sure HP, IBM, etc are right around the same ballpark or higher than Dell honestly. I honestly can't wait to have 5 virtual servers running on this new box and hopefully still have processor and memory to spare.