Try installing a DVD/RW drive into a G4 that wasn't bought from Apple. Their software will not run on it.
I disagree with you on the patent and BIOS issues. There is no reason that another company cannot make replacement boards with different chipsets...look at PCs. Apple cuts them off at the legs every time it happens. Do you remeber the clone processor producer that was taken to court by Apple...and what about the teenager? who was making apple clones. He ended up in court too.
Apple has some issues and they aren't patent or BIOS issues. They don't want to let anyone, except who they choose, develop for the Mac.
IIRC, there are some reverse-engineers for that. Apple has always been litigation happy. But for board designs, the PC revolution started when Compaq reverse-engineered the PC chipset. Since then, there's been a general culture of interoperability and open standards, although Intel was suing people over P4 motherboard clones.
A lot of work goes into inventing these systems, and it is a reasonable thing to not let people copy your work without royalties, or not copy at all. Lexmark didn't invent anything that had been copied, just someone figured out out to fake authentication with the printer and they didn't like that.
Apple has some issues and they aren't patent or BIOS issues. They don't want to let anyone, except who they choose, develop for the Mac.
Because they don't want the fragmented "plug and pray" that you get in the PC world. Losing control over Mac components would seriously degrade the quality inherent in a Mac system. If you don't like it, you can just vote with your pocketbook and not buy Mac. You can, of course, do anything you want externally with Firewire and USB.
And I say all this being generally a build-it-yourself PC person. I just understand the Mac point.