I was speaking at a conference not long ago on the future of mobile, and during my Q&A I heard a common question: “Will apps replace webapps?”. Hearing that question a lot, I have a standard reply: “Not everyone is going to want to download an app to get an insurance quote”.
I don’t think there is much debate over that. The web let’s you start, without any commitment, using an “application” without the the fuss  of engaging the app stores. It’s also platform agnostic, which makes things more efficient for developers (but that’s more about us as developers, and not about the user).
If that was the end of the story, you could say that web apps are “good enough”, in most cases. Why bother building an app, if a web app will do?
I do think you still need an app. It might not be for the new user trying out your service for the first time, but for the loyal custom who wants to keep engaged. I think app indexing  makes this hugely obvious, for anyone still in doubt. Your loyal customers will get your search results first, and they’ll be happy about it (hopefully).
App indexing is one example, but that’s just the start. The advantages of native apps will become too extreme to ignore, and your loyal users (the brand loyalists) will want them.
Build web apps to engaged and promote. Build native apps to maintain and delight. I don’t think we have the luxury now of not doing both.
 Can apps be used, in some reduced form maybe, without being “installed”? I’d be surprised if Google and Apple are not considering this a possibility.
 This is currently Google only, but make no mistake, this will come to iOS as well.