Presumably that's why films like the original (Christopher Reeves) Superman series and the Flash Gordon film were in part or whole played for laughs. It's interesting to note the variety of styles applied to the various Batman films over the years, from the really camp 60s versions to the dark and characteristic Tim Burton vision, which gradually slipped in the succeeding films into more jokey style.
The cinematic vision of Batman was regenerated in some style in the two Christopher Nolan films. Of course Batman has the advantage that the character and its origin is well known to most of the public, enabling imaginative retelling on film and on the printed page to succeed. Perhaps that is the problem with Watchmen - for the public at large this would be a new story, with new characters, many with a rich past (well, rich by the standards of a comic book serial) that had to be clearly laid out to the viewer.