There's a lot of "parodies" that aren't made, I'm sure.

The whole point of copyright laws is that you own the design and if someone is trying to benefit off of your design without permission, they are violating your rights. It is your work. You don't go out there and be (for example) an assembly-line worker, and someone else get's paid for it.

If you listen to a lot of Weird Al's songs, the majority of them, I'm pretty sure, are not parodies. That's because of the copyright laws I suspect. Sure, he might make his parody songs with little intent on getting permission first, but if the original creator has a problem with it and is adamant about it not being published, I'm sure those parodies are pulled from Weird Al's albums. And just because it's "known" he doesn't get permission for his parodies, doesn't mean he doesn't get permission. Don't be foolish and believe everything you read or hear on TV, kiddo. Weird Al is surely a businessman by now, and a big seller, it's doubtful he can afford to upset too many people.

But I think a significant difference between Weird Al's parodies and something like this Calvin and Hobbes likely ripoff, is that there is first: a mutual benefit; when a parody is made it advertises the original creator's work (there is a saying I have heard "you know you've made it when Weird Al Yankovic has made a parody of you song"). second: the backbone of most of Weird Al's parodies (i think) contain their own messages or premise, creating some kind of intellectual independence from the original source, which may make it more of a critique on society, or the human condition...or the ridiculousness of the original song.

Now you could say that the Calvin and Hobbes parody still falls qualifies, but that's where a court of law comes into play. A judge must ask: Is the parody-maker being truly independent in thought, or are they just outright saying "hey, people still love Calvin and Hobbes, so I'm gonna try to make money off of it."?

I am not a lawyer, a lawyer would probably have more points...but there's gotta be a line where the "parody" reasoning isn't actual reasoning, it's just simply stealing.