Quote from a friend who develops mobile apps: “Amdahl’s law generalizes nicely outside of performance gains to mobile software platforms. Once you’ve fixed all the bugs that are fixable, all you are left with are the fundamental limits of the platform, which users don’t understand.” (And he’s not even talking about iPhone.) Mobile platforms are certainly the most common situation where the same app running on two different phones will have different features, but I’d say it even generalizes to all software.