I'm one of the VASSAL developers. When GW forced the Vassal40k module designers to stop distributing their module, the most common complaint I heard was from people who used the module for planning out their Warhammer 40K armies. In other words, I was reading complaints from people who used the module to plan their purchases. With a way to test out armies before buying, these people are enthusiastic customers. Without a way to test out armies, these people are disinclined to buy miniatures. Another common complaint was from people who had no local opponents, but still wanted to play W40K. Same story here: If they can use their miniatures this way, theses people are happy to purchase some; if they can't, they won't open their wallets.
In the short run, shutting down the Vassal40k developers might look to GW like a good decision, but in the long run it's only going to lose them customers.