from what i understand, macs are not very easily upgradeable

They are in some ways. All recent desktop Macs, (IE the PowerMacs) have had PCI slots allowing migration of your devices that might be there. They use IDE drives now, and used SCSI in the past. (I actually just upgraded a Mac LC computer from a 40meg drive to a 9.1gb drive. Not bad for a 11 year old system) They also use standard PC memory now. And in most cases, 3rd party companies release CPU upgrades, extending the life of many Macs by quite a bit. For example, I can upgrade my G4 Cube running at 450 to a 1ghz machine.

The problem though with the CPU upgrades is that they tend to be pretty expensive because they don't make and sell a ton of them. But overall, a Mac can be as upgradable as a PC. There just aren't as many spare components around since Macs don't have a huge portion of the PC industry.