In following up on my entry about how to get a screenplay sold, I asked the other authors on the screenwriting yahoo group to provide a list of screenwriters who had made it by looking at the trades, deciding what was being sold and then writing a screenplay that fit those categories. He didn't. I in turn then provided a list of screenwriters (Woody Allen, John Sayles, Francis Ford Coppola, Paul Schraeder, Robert Benton) who did not make it as screenwriters using the studying the trades method.
In the end, my conclusion is that there is more than one way to skin a cat and one has to do what works best for oneself. My observation is that most make it based on who they meet or the connections they make and that as a writer, it's best to write something you want to write, and then try to find the market for it. But there are other ways and one is not necessarily any better than the other.
Whenever anybody says there's only one way to get into heaven, my red flag goes up.