People tend to expect the newer, narrower chains to wear out faster. People also don't have a good understanding of how chain wear and chain stretch happens, and don't account for the fact that, while old chains were indeed thick, they were also made of cheese. People made a big fuss about how 10 speed chains didn't last as long as 9 speed, and 9 was worse than 8, and so on. In reality, there's no appreciable difference between them as far as I can tell. Manufacturers do actually account for wear when developing new chains. The whole discussion isn't helped by the wildly varying reports people give for chain life; I am very skeptical that most people are as good at tracking component life as they think they are.