Here's the deal from my perspective...
I use my machine to make money. I do graphic design, illustration, and some photography. My current 2008 (3,1) cost me around $3200 fully loaded (with OWC RAM and HD's). I bought it in 2009 when the 4,1 came out.
In the 4 years that I have used this machine it has paid for itself countless times. I have profited from it's speed, reliability, and sturdy design. The only upgrade has been adding an ATI 5770 for about $250 (chump change in the pro world). It's a reliable computer and will probably last another year or two easily, and in the process I will make even more money with it.
So when it comes time to upgrade (I think a year or two), I'll find it extremely easy to write a check for $3000 - $4000 for a new Mac Pro (which by then will probably be a second generation). And I'll write that check with a smile on my face because I'll know I will be investing in several years of trouble-free workload... and more profits.
That's the calculation pros like me go through when considering equipment purchases. I pay a bit more for Apple products, but at the pro level, they have proven themselves to be impressive workhorses, so the initial cost is almost irrelevant when compared to the profits made over the life of the system.
I can easily understand the dismay some may feel at the cost of the higher-end machines (I'll be completely happy with the base model, so it's not an issue for me), but if the purchase is intended for professional work that is profit-oriented, the ROI should really ease the pain over time.