Actually, as it turns out, you were right, apparently residuals are another factor in what's preventing this show from being released on DVD... that, and there's even a problem with use of the theme song (like how Old School Vol. 3 omits SST's theme song). Compilation sets wouldn't do either, because apparently, to take parts of episodes for compilations is considered creating a "new" show, which means new contracts and negotiations would have to be drawn up.
Though, they're looking into having the show available for archive in libraries, which I guess means if your library carries DVDs (which mine actually DIDN'T until JUST NOW... dang, we're so behind the times), you might still be able to see it eventually.