I recall Watterson also battled with the newspaper industry over how his strips looked, especially with the use of colour in the Sunday strips. I believe he felt somewhat constrained by the format and you can see him stretching the format's boundaries in the Calvin & Hobbes strips, especially the Sunday ones.

I used to wonder why he never moved to doing comic "books" where he had more room to breathe. I've since come to believe that creative work benefits from some kind of constraint - a boundary to push against.