I click a link in Facebook or Twitter, I don't care about the URL. I care about content.
Sure, that link points to a URL, but I don't know what it is, and I'll never remember it. It could even be a really sensible URL, like http://odopod.com/blog/hack-days-2011-coming-november/ — but I still won't remember it. URLs are implementation details for content on the web, not content in themselves.
People want to share. They're probably doing it with Facebook or Twitter. Being able to share a link to content isn't dependent on a native or non-native experience, it's neutral. Even if your native app had a URL bar, you wouldn't want to copy and paste that into a thing and send that thing to someone, you want to press share and press a person.
Look, I love web apps — I even build one for a living! But users consistently appreciate native apps on iPhone (this doesn't apply to Android) because of the constraints of the HIG and the SDK.
/cc @jtaby
I basically agree. One of the biggest downfalls of web apps is that they feel "webby." Pages and and UI elements look broken until they load in, and you are constantly reminded that you are on a web page because of the ever-present browser chrome. It's the network lag that kills the experience, and native apps can completely sidestep it.
On the subject of browser chrome, native apps can completely remove it and drop the user into a UI that completely makes sense for the app. This mainly makes sense for games, but what about stargazing apps? Or photo slideshows? These apps cannot be held back by the browser's restrictions if they are going to be a compelling experience.
Native apps feel snappier. They feel like they are yours because you buy and download them. I too am a web developer, and that's because making apps for the web is way more fun and easier than making native apps. But only native apps provide the experience that users have come to expect, and HTML 5 is years off from matching it.
Web apps provide a better developer experience. Native apps provide a better user experience. We have a conflict of interest with the people who pay us.