To be fair, those rules were written before the canon hierarchy was established, so stating that the EU is canon and a correct answer (unless contradicted by a higher-level source) should be okay now. So let's get back on topic. I have stated that Qui-Gon reassured a panicking Obi-Wan that Luke would still be safe on Tatooine, due to the fact that Vader would never willingly return there. Remember, as far as Vader knew, the baby died with Padme, so he had no cause to wonder about where Luke could be hiding. You're thinking of "hiding" as "locked in a secure vault with armed guards 24/7." That's a horrible way to raise a child. Yoda and Obi-Wan wanted Luke to have as normal an upbringing as possible, because clearly the Jedi Order's methods of training Jedi from infancy had begun to fail. Giving like the solid foundation of love and family would be a great benefit when like finally became a Jedi. And ROTJ is where that gamble pays off. It wasn't a single fight that brought about the downfall of the Sith, it was Luke's love for his father, and his belief that there was still good in Anakin.