It's a shame people don't compare apples to apples.
When you compare the mac pro (workstation) to a cheaply build consumer desktop of course the cheaply build one is the one being the cheapest.
If you however compare the mac pro to a similar workstation (xeon processor based one), you'll see the price is in the same ballpark. (hard to match display cards, so a 1:1 comparison isn't easy).
Same goes for iMacs, if you manage to find a similar computer you'll find either lower specs or a price that is either slightly higher or slightly lower.
And for the macbook pro's you'll easily find cheaper laptops with older chipsets and lesser build quality. I have two pc laptops, one older acer travelmate that costed twice what my macbook pro costed new, and one new acer timeline 4810tz that I bought to fix up and keep at the univ so I can pedal there to get some exercise. The timeline can somehow be compared to the 13 inch macbook in price. It's 2/3rds of the price here of the baseline macbook pro, still it has a dualcore pentium processor, ddr2 ram instead of ddr3, a lesser quality display (still led backlit though) and the difference in build quality alone shows it's in different leauges.
So yes, macs are expensive computers. But they are expensive for a reason. The current models are well engineered, well built with modern components (beside in the end of the models lifespan) and without crapware to keep down the price. My next computer will also be a Mac, but what others choose I'm not that concerned about.
I've used cheap and I've used expensive PCs and still find the macbook pro to be well worth its price. And as a added bonus OS X is in my eyes far superior to windows. Linux is however my second choice.