There're potential privacy implications to using your call logs to build an implicit social graph. People have an expectation that their phone call records will remain private; look at all the trouble the NSA got into when they started spying on them. There's no such expectation when you explicitly give your relationship data to a third-party website.
Not to say it won't happen, but a bunch of things need to be worked out on the legal/ethical/cultural side of things before this is practical. As PG always says, social changes take longer than technical changes.
I have two contacts in my email, one is my Mom, and the other is my male boss. All of a sudden I am seeing lots of transgenderfication sites in my results. Mom?
It would still be a violation of privacy because it is crossing the friend/contact line.
Not to say it won't happen, but a bunch of things need to be worked out on the legal/ethical/cultural side of things before this is practical. As PG always says, social changes take longer than technical changes.