American Express has famously touted that “membership has its privileges.” For wealthy consumers today, those benefits total $9.2 billion each year, subsidized by middle- and lower-income households.As inflation-weary businesses raise prices to cover credit card interchange fees, the pain isn't universal, says research by Harvard Business School Professor Mark L. Egan. Because merchants charge everyone the same price regardless of how they pay, those fee costs are factored into prices for all sh...