That does depend entirely on defining Google+ as a content service rather than a communication service. And even if you can define Google+ as a content service, you can't define Gtalk and Gmail as a content service, and all Google+ subscribers are also Gtalk and Gmail subscribers.
Also note that the Directory service is Google Profiles, a service that pre-dates Google+.
I don't think gtalk/gmail is relevant. +Bradley Horowitz has debunked the myth that naming violations lock you out of everything:
When an account is suspended for violating the Google+ common name standards, access to Gmail or other products that don’t require a Google+ profile are not removed. Please help get the word out: if your Google+ Profile is suspended for not using a common name, you won't be able to use Google services that require a Google+ Profile, but you'll still be able to use Gmail, Docs, Calendar, Blogger, and so on. (Of course there are other Google-wide policies (e.g. egregious spamming, illegal activity, etc) that do apply to all Google products, and violations of these policies could in fact lead to a Google-wide suspension.)
+Tim Waugh This isn't a matter of account deletions, but legality under EU privacy law about subscriber directories. Google Profiles is a subscriber directory service, and it does tie into the communication services GMail and GTalk. Also, GTalk is actually integrated into Google+ as it runs the Huddle and Hangout features.