Quality Differentiation in Durable Goods Monopoly Always Yields Strictly Positive Profits

A monopolist producing vertically differentiated durable goods can offer in each period a sequence of price-quality menus to segment the market. We show that, contrary Coase conjecture for homogeneous good monopoly, thanks ability produce goods, all Markov-Perfect Equilibria, profit that cannot commit future is bounded below by strictly positive value independent discount factor.