I wouldn't call it "one humorous line". Always in the shareware demo, when you finish the game, there are 22 screens (2 of them unavoidable) publicizing the other Jazz 1 episodes; when you quit the game, other 3 screens (1 of them unavoidable, 2 if you use DOS).
So whenever you play the game you have to see all those advertisings, and if you pay attention, you'll see how cunningly they are written and placed: in most of the cases sooner or later they start to convince you to buy. Now try to imagine the effects they would have on a six-year-old child that plays this game quite often: of course, it isn't brainwashing, but it still remains a merciless half-subliminal advertising, in my opinion. Am I wrong?

But this is only an example: there's another one you all know.
Jazz Jackrabbit has been abandoned since a lot of time: now Epic Games develops much more advanced games (Gears of War, Unreal, etc.). So, now the Jazz Jackrabbit 2 engine is completely useless, since they don't develop side scrollers anymore and anyway it's quite buggy. But then why the hell don't they release the source code? Because, as someone said, their lawyers say they must defend the intellectual properties of Epic Games? Even if they are of no use? (I mean, the intellectual properties, not lawyers, that's quite a different matter)

At least they make good posters!