Do you have the source? A poll or a study? My experience is that people that prefer flat bars stay with them. The problems that the op is describing is solved by a simple seat adjustment. For commuting and utilitarian riding around the city, flat bars and flat bars with bar ends are ideal. I would agree that some people will switch to drops, but "most people graduate" to them is a stretch. I went the opposite way, from drop bars to flat bars and am quite comfortable and happy.