Might be appropriate to adjust for inflation. Here's a calculator that is useful for that:
http://data.bls.gov/cgi-bin/cpicalc.pl
So the high end G4 listed at the site you link to (which comes closest of those listed there to being configured like the entry level quad core Mac Pro) was listed at $3274. Plugging that into the inflation calculator yields $3882. That's more than the 3.3 GHz quad core lists for today (with base configuration), and more than the entry level 8 core machine.
The first Mac I bought with my own money was a Mac II ci, which I bought when that was current. Price was probably not that much less than a quad core Mac Pro today (although I don't remember exactly what it was -- I could be wrong about that).
In Sept., 2001, I bought a dual 800 MHz Power Mac with 128 MB of RAM (subsequently upgraded to 1.125 GB), 2x60GB hard disks, superdrive, GeForce2MX video card, SCSI PCI card for $3469. Plugging that into the inflation calculator yields $4273.63 -- close to a dual 2.66 GHz 8 core Mac Pro. Monitor (22" LaCie Electron blue III) was $999. This is still my current Mac -- still works (but painfully slow with some current software), and I can't upgrade some of it because much of what I want is Intel only. So I will be buying a new Mac Pro, and I will probably wind up spending an amount that is similar to what I spent 9 years ago. And I will have a much more capable system.
Macs have been considered expensive (relative to non-Mac PCs) from the time I first got involved in buying them back in the late 1980s (Mac II, IIx, IIci, IIcx, purchased for work). I don't think this has changed much. Nor has the complaining about prices on web sites like this one.