For many use cases (games, highly interactive experiences, camera or microphone using app, etc.), a native app may just be better, and guiding users there might be a better experience and a better conversion funnel.
Yes, you can make a website mobile friendly, but that doesn't mean it will be as good as the native app.
In the context of forums though, its entirely true and accurate.
If we were talking about apps, as in things that require more than an internet connection to work, I would agree with you.
Just because you can make it an app, doesn't mean you should.
When it comes to websites that try to force their app upon you when visiting their mobile website, my experience has almost always bee n the application is as bad as, if not worse than, the website's functionality. This gets to my point that if your developers are not capable of building a decent mobile friendly website then they are probably not any better at building an app.
Also I hinted at the fact that in many cases these apps appear to be designed to track users and invade users privacy. Why else do so many need access to contact lists and more when their functionality doesn't remotely require it.
http://mobile.weather.gov/ would disagree with you.