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I hate to burst Metacogniziant's bubble, but the questions on Who Wants to be a Millionaire? are not all that different from those on Win Ben Stein's Money.  The questions worth under $1000 questions are easy and mostly pop culture-ish, to be sure, but after that the questions are pretty reasonably spread out through a variety of categories.  Especially in the highest three or four questions--obscure science and obscure history become the norm there. Your blanket claim that the questions on Millionaire are all pop culture-related leads me to believe that you jumped to conclusions about the show after watching it for about thirty seconds.

Another reason why Win Ben Stein's Money seems harder isn't because of the questions, but because of the format--free response instead of multiple choice.  I might have trouble coming up with the right answer off the top of my head, but if I had a list of four choices to choose from I'd be able to pick the right answer out.

The discontinuity in the prize amounts proferred comes more from the fact that Who Wants to be a Millionaire? is backed by a major network (ABC), while Win Ben Stein's Money, being on a cable station (Comedy Central), has a budget an order or two of magnitude less.  If you look at any game show that isn't backed by a major network and/or broadcast during prime time, the prise money rarely gets above four or five digits.

And if you want to compare two shows on major networks--the same network in fact--Jeopardy! gives out between $5,000-$20,000 to each winner, and the average winner of Who Wants to be a Millionaire? doesn't take home substantially more ($16,000 and $32,000 seem to be the median values).