Many, many games published these days have a VASSAL module available before they go to press because game designers are using VASSAL for playtesting. In the wargaming world, there are publishers which actively promote the existence of VASSAL modules for their games (GMT and MMP are the two big ones which come to mind, though there are others as well), some which are indifferent, and a few which are opposed. The impression I get is that the availability of VASSAL modules increases sales for publishers which aren't in opposition to it.