Unfortunately, that's true. That's one reason why I don't really like how Viz treats most of its anime series. I would love it for them to finish Hikaru No Go, especially since they actually finished dubbing it and they only had a few more episodes to put on Jetstream, but Jetstream ended before that could happen. I also would have like them to continue Mega Man Star Force since I thought that it was a better and more interesting Mega Man series than NT Warrior. I didn't hate NT Warrior or anything like that, I just though Star Force had a more interesting storyline.
While I can understand that some of the DVRAB for these series might not be selling that well, especially compared to some of their other series like Naruto, Death Note and Bleach, I also think that it really isn't a good idea to stop the DVD releases in the middle of the series. Considering how expensive it is to get the license for a series, to dub a series and then releasing the episodes on DVD, just sitting on the licenses for series and not really doing anything with them would probably cost them some money as well.