I don't think that walled garden is technically applicable to the wild of the internet. Apple dictates (negotiates) the terms with the iOS carriers and can ensure that direct connections between iOS devices over the carriers is possible for the apps Apple wishes to whitelist.
Facetime over cellular wasn't enabled as a feature until last year, which means during the time period discussed in the patent lawsuit (last year) it was either non-existent or very new with minimal usage. Some carriers still don't allow it at all. For the most part it is/was a WiFi application meaning Apple has no special relationship. I'm pretty sure other applications will show similar statistics.