It's not a link, so it's not officially against the rules!
Though it skirts that grey area just enough that I'm sure Apple wouldn't be too thrilled about it.
Yep.
Didn't the Amazon Kindle app have this same problem?
They weren't allowed to put a link to the Kindle Store to sell books... so I thought they told people what to do instead.
I don't have the Kindle app installed so I can't verify.