The field service and publications are not really for getting new converts these days. They are for keeping the members they already have. Look at some of the recent articles on what to do if somebody leaves, wives obeying the men and so on. So yes, having sex is how Watchtower gets new JWs.
This certainly seems to be the case. It seems that more and more people are researching the Witnesses online before they even attend any meetings.
It's funny. When I was a Witness, I never heard any of the "worldly" people who knew I was a Witness, say anything to me that was unflattering about the religion. Now, when I tell people that I know that I am a former-Witness; they feel much more free to share their honest observations with me. A few of them told me how bizarre some of the Witness beliefs are. And these aren't some obnoxious, crass, or obstinate people. These are people who are very kind, decent, loving, and law-abiding.