my comment to them is that they are mucking around with apps/settings too much in windows that they will not be able to muck with on the mac

Do you really think that your grandma (replace this with the owner of the computer you're constantly going over to fix) is dorking with the registry or replacing hardware drivers? No. Other than those things, which I'd consider ``under-the-hood'', what should allow you to make your computer less usable? IMO, nothing. But Windows becomes less usable even if you do nothing but run the same single program over and over.

Ever tried managing appletalk?

Ever tried managing IPX/SPX? It's just as big a PITA.