"As far as proof, how about the fact that iMacs are pretty close to un-modifiable, anything breaks and you have to ship it back to the company."
Well, that's pretty lame proof. Most PC manufacturers require you to send their machines back to them or have it serviced by an authorized repairer when there's a problem, or risk voiding your warantee. Apple does the same thing. If you really want to get inside the box by yourself, you still can. The only major difference between an all-in-one and a regular PC components-wise is the monitor. Sending the computer in for repairs is a problem specific to all-in-one machines only if the monitor is broken. For any other part, the manufacturer would most likely want you to send your whole computer back to them anyway, if your computer was an all-in-one or not.
The iMac is designed for people with no previous computer experience. Seasoned Macintosh veterans such as myself buy Power Macs. Personally, iMacs are not for me, but I don't look down upon them. The iMac DV Special Edition especially is actually an excellent machine and more than enough to last a newbie for a while. It's also a good game machine, unlike the first generation of iMacs. As for being a "tech support nightmare", the iMac was specifically designed to be the exact opposite. The hallmark of the machine is its simplicity. The idea of the machine is that you'll never need to call tech support, because your 3 year-old could set it up blindfolded.
SGI is great for making Star Wars, but most small companies would rather buy a machine that can do graphics efficiently and doesn't cost them $12,000. As a graphics professional who has done graphics for companies such as DuPont, I can tell you that the vast majority of clients aren't looking for artwork that pushes the cutting edge. They just want you to make something cheaply in Freehand that looks great and keeps their art budget down. Macs are perfect for these kinds of jobs, and it's these jobs that dominate the graphic arts industry. Not everyone's trying to make Toy Story 2. I'm not knocking SGI, but it's a different tool for a different job.
Most Mac graphic artists use Power Macs, so I'm not sure how graphics got lumped into this node anyway.
Of course, you're free to your opinion, but you shouldn't base your opinion on inaccurate facts. And that's my $.02.