I think the Apple rule they're referring to is that if you have an in-app transaction, you're not allowed to reference the fact that the transaction can be made off-app (which would avoid Apple's 30% cut). It's not quite the same, but similarly draconian in that it restricts what you're allowed to say (as opposed to what you're allowed to link to).
That’s one part of it, also if you sell say ebooks or MP3s, you can’t sell them in-app, but also you can’t even provide a link in-app to buy them using the mobile browser.
I don’t want to derail this conversation with App Store policies, but the notion of policing links isn’t great, especially for a social network.
Not only that. There are a lot of things you can't say on the App Store. Pretty much anything critical of App Store policies or mentioning alternative platforms as text in your app (rather than user generated content) is likely to get you the boot.
