With all due respect (and I mean that, because I enjoy Worms) the choice to take an artistic and/or personal work and make it a commercial product is, as stated, a choice. Unless you manage to get a contract where you retain full ownership of your IP, you're making sacrifices to whatever your personal meaning for it might be when you mass produce it and stick it out on shelves.
What you need to understand is that when we are talking about a comercial product, ultimately, it is the consumers who decide what a thing is, not the creators. And, ultimately, that is for the best (in comercial works, specifically) because the people get what they want, and the creators get more money to use towards future works and dreams.
If Katamari had been created as a free download, with Takahashi in complete ownership, then my feelings on the entire thing would be very different, I assure you.