Considering that you can only run OSX on Mac computers, Apple can have a lenient license policy. Theres no garage workshops turning out generic Macs with off the shelf parts and making pirated copies of OSX to sell with them. That would change if Apple decides to sell OSX as a stand alone OS that can be installed onto any PC. Of course that would open Apple to all the crap that Microsoft and Windows has to put up with.
I like windows and PCs because I can tinker and tweak the system, I just installed a Lightscribe DVD burner in my system, I dont think you can change the Superdrive in the iMac, or go to New Egg and get the latest video card.
Im not an Apple or Mac hater. I have an iPod Nano and use ITunes nearly everyday and I have recommend to my father that his next computer be a Mac, especially considering Windows software can run inside OSX. I would buy a Mac desktop if their machines suited my purpose and were easier to upgrade. I am considering a Mac laptop in the future, but my good old Compaq is working just fine for me now.
The tweakability of the system is something that I've found is very important to Windows and Linux guys, much more so than everyday users and Mac people. I'm in the category of viewing it like working on a car. Some people enjoy it, I do it when I have to.
You're correct about the iMac line. They're almost like a laptop, as far as trying to replace components. OTOH, I've got a firewire external hard drive and a firewire DVD burner hooked up. On the newer versions you can go USB 2.0, but mine goes back to the days before USB 2.0 existed, and just has USB 1.0. I had a Lightscribe drive, but wasn't that nuts about it. If I burn CDs or DVDs that need a custom front, I'm usually burning a bunch of them for an event photographic shoot, and the Lightscribe drive I had took about 30 minutes to do one. I also think using the Lightscribe feature a lot shortened the life span of the drive, as I burn a lot of CDs and DVDs, and using Lightscribe put the same amount of wear on the unit as burning each CD or DVD twice.