Quality-ladder models in the innovation literature describe how firms try to outdo each other in research and development in order to become market leaders by producing the most advanced products. One log-standing result of this literature is that leaders have no incentives to innovate because it would cannibalize their own business, a result that flies in the face of overwhelming evidence to the contrary.
Hélène Latzer builds a model where firms can price discriminate in a specific market. The difference with standard quality ladder models is that consumers differ by wealth, preferences are non-homothetic and only full units of technology goods can be consumed. In standard models, it is always winner-takes-all. Here, because a slightly obsolote product still has a market, a market leader may still want to innovate to capture also the market for the second-best good.