If that was the label that went on the 17+ apps that are 17+ for third party content that would be fine - like for apps that would get a rating like 4+ otherwise. But it's not. Check out http://itunes.com/app/downloader for an example. The 17+ label for apps with mature content in the app and the 17+ apps rated as such for possible access to mature content are not even the same - at least the former is labeled only for the kind of content that is in the app, not the whole free-for-all.
...not to say that the 17+ rating should serve as the rating for "there might be adult-themed third party content", but that maybe apple should have one rating for the app itself and then a warning for the third party content...and a whole section in parental controls to enable/disable these particular apps with these warnings instead.
Alternatively, I wonder if Apple could put a hook into the iPhone's browser api such that any use of a browser in third-party apps can be restricted from parental controls.
Unfortunately the browser isn't the only place to access user-generated content. Take for example a Twitter client, just by nature of being a Twitter client and theoretically having access to the public timeline with mature content is enough to get a 17+ rating. Or...name any app that would need a browser built-in, presumably because the user would come across many links while using the app (and of course the dev wants to provide a better user experience via not having to quit the application)...where would the links come from? It wouldn't be just the browser that needs restricted.
...not to say that the 17+ rating should serve as the rating for "there might be adult-themed third party content", but that maybe apple should have one rating for the app itself and then a warning for the third party content...and a whole section in parental controls to enable/disable these particular apps with these warnings instead.