A friend asked me if I could make an application that displays the contents of his website. The idea is to use the AppleStore's communication.
I searched and the only "limit" that I see is that we have no right to make a commercial application.
Have you ever tried to send an application in the same type to Apple?
Apple has tended to reject these in the past.
You're entirely free to make commercial apps, there are plenty in the App Store.
If the app you contemplate does nothing that Safari could not do, then it faces rejection. How would you feel if you paid $0.99 for an app that was nothing more than a bookmark for a web page? How would you feel if you just spent the time to download a free app that was nothing but a bookmark?
To be accepted, the app must provide some value to the user beyond just directing them to web site. For example, there is nothing wrong with making a widget type app that creates a custom mobile interface for a web site. By making the site easier to navigate on the iPhone, you've provided the user some value.
Back in the first year of the iPhone, the App Store got spammed with apps that did nothing but display several different sites and which provided no actual value i.e. Safari did just as good of job. There were a lot of complaints and Apple has looked for that ever since.
The key idea here is that you should be providing a benefit to the user and not just yourself. You need to think why another person would benefit from having your app. If you think of the app of a means of tricking people to your web site by making them think they're getting something more than just an elaborate bookmark, then your app most likely won't be accepted.
Apple showcases websites that work well on the iPhone. You can submit your website. See http://www.apple.com/webapps/
It's not as high-profile as the App Store, but maybe it will draw some traffic to your site.