I have a Dell Inspiron E1505 that is three years old, it was loaded with the fastest processor, most memory, 7200 rpm harddrive, x1300 video card, best LCD screen(15" 1680x1050). I love the machine.
Looking on ebay, it appears I could get around $400 selling it now.
Ok, so I looked up similar vintage MacBook Pro, looks like they sell for $1000.
But here's the thing. I looked at the MBP, and at the time for the same configuration it was $2400. My Dell was $1200.
$2400-1000 = $1400
$1200-400 = 800.
Yeah, my Dell wasn't quite comparable to the Mac... not as fast of video, heavier, etc. But it did what I needed. So I agree with the original point that if you price out what you need you can get a cheaper machine and I don't think resale makes up for the difference.