Many more developers are answering that question with a enthusiastic, "Yes, moar marketing plz." Why shouldn't they, when a open beta is a great way to let people get a hands on with your game before it comes out. If your open beta is in fairly solid shape for most people's systems, the good word-of-mouth will pay off. That pre-launch buzz is going to net you more sales, and isn't that what you want in the long run?
But this whole controversy isn't getting started up because no one realized that open beta could also be spun as marketing. No, this controversy is being started up because many of Funcom's actions regarding the Age of Conan open beta were blatant marketing strategies. Yet, all of us were scratching our heads when a bomb finally dropped -- the open beta used a prior version of the AoC client?