What makes a pro body?

It seems to me we have a clash of visible quality vs market snobism. Let me explain: customer has a choice of buying a 16MPx image and a 36MPx image; customer will go with 36MPx. But, assuming both images correctly frame the subject, there is no way to see a difference between the 2 without pixel peeping. So, from practical stand point a 54MPx d4x will result in an image that does not look too different from D800 or even D4, unless people pixel peep. Is our population really so dumb as so justify the cost and provide ROI on a 54MPx camera vs existing 16 and 36MPx?