Bill Watterson objected to derivative works - ie C&H baseball caps, cartoons, fridge magnets, bumper stickers, colouring in books etc.

A search engine isn't a derivative work (at least in the way that Watterson dislikes). The objections to the search engines come from the publisher under the guise of copyright infringement. I would assume that whilst they can turn a blind eye to a fan site with the occasional infringing comic strips, they can't turn a blind eye to a search engine which contains the entire script of C&H.

If that is so then what is with all the urinating Calvin stickers? Every time I see one I feel like my childhood is being wizzed on.

Those stickers are derivative work - unsanctioned and thoroughly frowned upon derivative work.