"Most"? Really? Most of the XP machines I know of are being used like any normal desktop machine: email, browsing, office, thumb drives, etc.
I know things are different with industrial machine control, they might be different at my doctor's office, and so forth. But I don't think those special situations add up to "most". Not yet.
And the dentist office is one of them, actually. Anyway, I may be wrong about this right now, but as you note, in a few years, when the support dies and nothing works on XP any longer it will still thrive in environments I describe.
I know things are different with industrial machine control, they might be different at my doctor's office, and so forth. But I don't think those special situations add up to "most". Not yet.