We must ask ourselves, when is something a Knock-off? On twistypuzzles.com a factory made Windmill cube is seen as a knock off. Mr. Okamoto did come up with the idea, but it's not patented. Why? Because it's not new. It's an existing product with some pieces cut off, it's nothing original. You can't make a minor adjustment to an existing product and patent it. If I would "mod" a 3x3x3 by cutting off a corner, that's not an original idea, nor can I claim to own the concept.
Also, like said before, if a company comes up with a product and another company copies it but makes it better, the original maker should answer to that. The YJ 6x6x6 seems to be much better than the original V-Cube 6x6x6. So the V-Cube company should improve their 6x6x6.
YJ did break a patent, but that doesn't necessarily mean it's immoral, in my opinion. It doesn't just become moral to copy the moment a patent runs out...
So if the windmill cube is an original idea, than so is the YJ 6x6x6, they're both slight variations on an existing product....
I seem to be contradicting myself, but I'm actually quite indifferent to all of this. If I'm out to buy a product, I'm getting the best version for the best price. If that happens to be a knock off, so be it.