In this case, selling out (even a little) would have helped.
By refusing ANY merchandising or licensing beyond reproduction for authorized collections, Bill Watterson not only retains a huge amount of (ostensible) control over the characters, he also retains the huge number of responsibilities with regard to copyright. Plenty of popular characters are subject to misappropriation, but if the onus of hunting them down is not spread among various interested parties, then the original creator gets to shoulder the entire burden.
Would you rather be under siege by yourself, or share the cost of defense among others who benefit by assisting you?
BTW, @thirdworldtaxi - Sorry about misinterpreting the intent of your original post.