In my humble opinion, PC and "personal computer" are issued from "IBM Personal Computer" which is a trademark.
When you talk about a PC, you think that it have a x86 processor and a "bios compatible firmware".
And because of IBM PC was sell with MS-DOS, by extension a PC is supposed to be "Windows compatible"
Otherwise, how do you call what I call a PC and what should be the difference between microcomputer and personal computer ?
In this way a PS3 is not a PC, even if it's designed to a personal use and if you can do the same task with it (by installing linux for example).
In this way too, iPad, iPhone and other handheld computers are not PC.
So I propose to replace "personal computers" by microcomputers to avoid this confusion, and to specify eventually this common confusion.