I think a large part of the respect for Watterson comes from the fact that he never "sold out". He made his comic and when he felt it was done, he stopped. He didn't do a Saturday morning cartoon, and lunchboxes, and t-shirts, etc. What merchandising there is for C&H is, afaik, unlicensed.
Watterson is an artist, and he did it for the art, not just to make money. It lends a lot more credibility in some people's eyes.
It also shows that the strident anti-commercialism stance he takes in many of the comics isn’t just talk. He actually believes and lives it.