It isn't really censorship in a strict big-controlling-bigbrother-government sense.
If a government is censoring, they block completely 100%. You will not be able to freely say what you want.
Here, you can definitely say and do what you want (within the law) -- Just not on an iPhone.
If you own a website with a forum on it, and you don't allow certain links to dubious content in the comments, that isn't really censorship either, is it?
I'd say this is definitely censorship. It's censorship chosen by those who choose to purchase an iPhone. It negatively affects those who have an iPhone and especially those developing for the iPhone. Yes, you can make an argument that one doesn't have to own or develop for the iPhone, but for the developer, that's over 40% (I believe) of the mobile phone market in the US. That's a huge customer base to ignore simply because it's risky to develop iPhone apps due to Apple's censorship.
Also, iPhone apps are generally useless outside of the app store. Sure, someone with enough technical know-how can install them, but for all intents and purposes, they have no value if they're being censored. That is very different from moderating a website. There are billions of websites and only one app store.
If a government is censoring, they block completely 100%. You will not be able to freely say what you want.
Here, you can definitely say and do what you want (within the law) -- Just not on an iPhone.
If you own a website with a forum on it, and you don't allow certain links to dubious content in the comments, that isn't really censorship either, is it?