IMO, you need to be just as prepared with your questions to ask them as you are with your answers for expected questions from the prospective employer.
As Mathew Foscarini pointed out, my leading question is "what's your development process?" And then I start drilling in from there based upon what I hear. I'll ask about source code control; what their experience has been with that product; defect tracking; how rigorously they follow whichever development process they said; how they handle last minute change requests; etc...
The interview is a two way street and you want to make sure that you agree with the overall development methodology of the shop. I'll admit some of my questions are biased based upon areas I've been burned before, but that's just human nature.
Specifically on "Simplicity": I think you're going to have a harder time interviewing / asking for this concept. Full disclosure, I didn't watch the presentation (TL;DW), but the concept is not that unique. Apple products are well known for simplicity in elements but powerful in functionality. As more and more iProducts find their ways into consumers hands (which includes development managers), we'll see more and more of a trend towards minimalist design with powerful functionality. It's actually more expensive to design and code, but the converts will swear it's worth the extra effort.
Find some companies whose products you admire and target them for getting an interview / consideration for employment.
To directly answer your question - I don't think you can really "interview" for simplicity / simple artifacts, but you can find the companies that are following that approach.