You can take a cigar box, attach it to a 2x4, stretch some strings from one end to the other and call it a guitar. Partscaster is merely verbal shorthand for a guitar that wasn't assembled by (in this case) a Fender factory. We are, as we used to say in my youth, "ate up with it". We obsess over all things Fender or Gibson. I know when I bought my first Strat it never occurred to me to ask if it was a partscaster (it wasn't), but now every guitar has to go through a 55 point inspection before I'll even consider buying it. And if I find anything changed or modified, it's going to be reflected in what I'm willing to pay. Maybe it's just an artificiality invented by Fender and Gibson marketing as a tool to inflate keep their prices maximized.