Mac peeps, what am I missing?

[Ghoulish Delight]

Okay, it's getting close to time to buy a new computer. Our dell is almost 4 years old. It's still useable, but it's at the point that it can't handle the newest software, and it's having general performance problems that can probably be attributed to things like the age of the hard drive.

I'd LOVE to buy a Mac this time around, but I don't know. I priced a Power Mac G5 vs. a Dell. I can get a mid-range Power Mac for just over $3k, vs. a high end Dell for under $2k. Yikes. But then I took a peek at the iMac. Here's where I need to know what I'm missing.

I looked at the iMac. I looked at the highest end iMac (the 20"). Added a little RAM, added a wireless keybaord. It's a 2.0Ghz processor whereas the Power Mac I priced is only 1.8Ghz. Everything eles I speced out the same for the Power Mac and the iMac. And the iMac is about $900 cheaper! Same everything, same size display, faster processor, $900 cheaper.

So what am I missing? Is upgradeability the only sacrafice? What about things like number of USB ports? Reliability (I priced Apple Care into both of them)? What gives? What makes the Power Mac $900 better?