On every XP install that I've seen from every major OEM (Dell, Compaq,
Gateway, etc) fast user switching is on by default and every user is
an administrator. Not "on most"; on every single one.
Furthermore, these machines don't have actual XP OS install CDs, they
usually come with "restore" CDs that just return the PC to this same
initial state if they're used, which they almost never are.
I have never seen a home user, that is to say change that setting or
create a user who is actually just a "User". Not once, ever.