Actually, that's backwards... You know that something is well designed precisely by pretending to be an idiot, and asking yourself if you still know what to do...
That's a very rudimentary view of UX. If I'm writing an app that helps radiological engineers calculate radiation dose, should I pretend to be an idiot? Likewise, in a world where kids have grown up with these devices, should we still think that way about UX? I think we can give users some benefit of the doubt. Each app should have a design that reflects the purpose of the app. Consistency is not always the top priority in UX.
I'm not saying that's the only step in design...
In my attempt at brevity, I lost the nuance.
The point I was trying to make is that if you're taking the view that your users need to have a significantly higher than average the level of knowledge in a domain area (i.e. equivalent to the knowledge of the domain area that the product designer has), you're going to end up with an un-usable product for the left end of the bell curve of your user population.
That left end of the bell curve is relative (as you point out) to your user population, but exists nonetheless - an "idiot" radiological engineer is not an idiot in relation to the general population, but is one in relation to the 99th percentile best radiological engineer (and, hopefully, in relation to the radiological engineer building your product).
What I was trying to say is that a well-designed UX requires that the 1% "idiot" of your target user population still knows what to do...
Gotcha, I'd agree with that. I have some bitterness extending from sham "UX Hackers" selling e-books that basically boil down to pretending to be an idiot, and thinks that is enough. :)