Re: This is probably about the OS
@Mark Dempster,
"I don't think there ever was a PC standard set;"
There was the PC System Design Guides, see this Wikipedia Article. PC98 set out a lot of the standard hardware, things like ACPI, how PXE boot should work, how plug'n'play worked, etc. The tables of contents at OpenLibrary is quite revealing. That lot coupled with a few chipsets from the likes of Intel, AMD, NVIDIA, etc. made PC hardware what it is today (basically it's all PC2001, just evolved a bit), whilst still allowing a diversity of devices. Pretty useful stuff, actually.
What makes Apple's machines different is that they don't really follow everyone else's common understanding of what makes a PC a PC.
If you think that remembering MCA shows your age, forgetting PC-98 shows worrying signs of a different sort...