When visualizing successful product adoption, we often use s-curves to show the value. I believe we find a similar trend if we look at types of interactions on devices. At some point the software tools, such as copy / paste, or taking a note, become a utility and a commodity.
If we look at iOS, we can decompose the layers that support developers. Starting back in the days where iOS had a vibrant JailBreak community, copy / paste functionality started there and eventually made it to the OS and various apps. Common tools like Reminders and Notes, started in the AppStore but eventually ended up as core “OS” level applications. Apple has a tremendous amount of app usage data and obviously invests in bringing highly successful apps to everyone by commoditizing their functionality. Every WWDC there is usually a list of apps that Apple has killed.
The pessimistic view is that Apple is only doing this for their own capitalistic self interest. This definitely rings partially true. However, the way to compete with commoditization is through innovation and integration. With Apple taking these common tools and making them commodities, it forces an innovation incentive in the AppStore, arguably much faster than if pure market dynamics were at play.
Siri is another angle, since it forces developers conform to a standard API for app interactions and discovery, it introduces an interesting abstraction for users switching between tools. Perhaps, longer term, the path from AppStore to Utility will only accelerate, or at least become more opaque. Instead of a different app, Siri can simply "do the task", like sending an email, or play a song, because it normalizes the interface to a larger degree than UI interactions. App discovery and installation are still possible, and I'm unsure if UI interactions are habitually stickier than voice interactions. One would think that with smart NLP, voice interactions would be more portable across different applications, or contexts, but I haven't experienced enough of these to have a strong opinion.