Considering the awful selection of titles for the other systems, I'm not surprised that TG-16 games are selling well. For what's available overall, you get the most bang for your buck.
I think maybe part of the reason TG16 games are doing so well is because not too many people had the chance to own a TG16 as a child. Whenever I mention turbo grafx to people that had Nintendo and Sega systems, I often get that head tilt action like a dog does when it doesn't understand something (tilt to the left, with "errrr?" expression). Anyway, I think many are like, how do I get that goodness in me?
Well, you can get most or all of the VC Genesis games on the Sega Genesis Collection for PS2, with special features and such, for the price of like 2 - 3 VC Ganesis games. And those VC Genesis titles are still pretty pitiful considering the Genesis' library.
The SNES VC titles are even worse.
But most of the TG-16 games are pretty good. I hope that they continue to bring out only the better TG-16 games until they start running out of titles.
But when they've exhausted the number of decent TG-16 games, I hope they move on to bringing us decent PC Engine games next, even if they aren't translated. There's got to be at least 50 nice PC Engine HuCards that are totally playable without translation.
The only problem would be all the licensing rights issues with non-Hudson releases...