Is this any way to sell a screenplay?

Over the last week, I got into a tit for tat e-mail dialog in one of those yahoo groups about how to make it as a screenwriter. One person posted an entry that posited that if a screenwriter was serious about earning a living in the biz, a writer needed to read the Trades (such as Variety), see what studios and productions companies were buying and write a screenplay to fit what they were looking for. At first there seemed something logical about it all, but I was troubled. I couldn't really argue against it, but I did mention a few things that I thought was wrong with his approach: such that once the Trades figure out what everyone is buying, that usually means the buying spree for that type of film is over and people are moving on to something new; that it's not just that easy to right something to fit a predetermined category (I mentioned the scene in Sunset Boulevard where the screenwriter was writing something he thought was what everyone was looking for and it was just that approach that doomed his writing--and see what happened to him); and that in actuality, wouldn't it be much more logical not to write what the Trades said producers were looking for now, but to write what the next big thing was, which is no easy feat. I let the matter drop at this point.

But then I started thinking more about it. I started going over all the bios I had read of writers; the interviews I had read; the articles; etc. and I just couldn't come up with any writer who had sold screenplays or got them done on the basis of studying the Trades and then writing a screenplay based on what the studios and other producers were buying. I decided to e-mail the group and ask if the original person who suggested this method of marketing one's work could come up with a list of writers who actually did it this way. I shall update the blog as I hear.