What is the Web for?
These are the wrong questions. The question is not “what is the Web is for”, but rather “who is the Web for?”
And of course, the answer to “who is the Web for?” is people. People who need to seek out information, to complete tasks, to buy things, to contribute their thoughts, to communicate with their fellow humans, to share their gifts with the world, to create, to consume.
The Web is a continuum of experiences served to a multitude of people on a dizzying array of devices, browsers, and environments.
So rather than foolishly attempting to draw a line in the sand between “sites” and “apps”, instead think how you can create experiences that enrich the lives of the people that interact with your creations. But as you create those experiences, work with the Web’s grain rather than fighting against it.