I'm typing this on a Macbook that no longer has its original RAM, hard drive, or keyboard/trackpad. The RAM and hard drive upgrades didn't break any sort of warranty and were rather trivial.
The Mac Pro is certainly not the only apple computer to modify. It is only the easiest to upgrade. Just because an upgrade isn't easy or encouraged doesn't mean you can't do it.
I'm typing this on a Macbook that no longer has its original RAM, hard drive, or keyboard/trackpad. The RAM and hard drive upgrades didn't break any sort of warranty and were rather trivial.
The Mac Pro is certainly not the only apple computer to modify. It is only the easiest to upgrade. Just because an upgrade isn't easy or encouraged doesn't mean you can't do it.