Are JWs restricted from expressing things in their own words?

I've been wondering if there is any _official doctrine_ held by Jehovahs Witnesses that would restrict them from talking about their faith in their own words? I have noticed in my interactions with them (through everything from talking to door to door missionaries to hanging out with the families of some of my friends to reading their postings on this site) that instead it is very typical for them to use the exact phrases and constructs found in officially sanctioned publications, often preferring to quote these sources (Watchtower, etc.) wholesale rather than writing or otherwise articulating their views in their own words. As a Reformed Protestant, I believe there is great value in using words and constructs whose meanings have become well defined and have been tested through time. In particular, I will even direct people to re-frame their own questions in the words Scripture uses for given topics rather than their own because I think this will help bring clarity to the issues they face. At the same time I see great value in meeting people where they are at -- in speaking the same language -- and articulating eternal truths in ways that people relate to and that specifically match the important issues. However much some Theologian may have said something better than I and I might quote them, still I do share the Gospel and articulate my faith to people using my own words. This seems fundamentally different from the interactions I see from JWs. When you ask them a question, they will seem reticent to stray from a specific track and try to find the closest matching stock answer from their repertoire. Or so it seems. My question is, is that an official stance? Is there a specific teaching or doctrine that binds them to operate this way? Or perhaps a more general doctrine that leads people to that conclusion even if it isn't a requirement?