Batman's a bit of a cheat when it comes to superhero design. You mentioned the ears. Not only do they give the character a recognizable silhouette. They speak to the archetype of people with horns adding a level of supernatural malevolence to the character. He's a wonderfully plastic creation, because in the end if all you have is a silhouette with pointy ears and a scalloped shadow, you've got Batman.You can ask pretty much any comic book artist who takes the time to study design, and get the same response. I’ve heard it from a lot of guys. In the case of Cliff and the Wonder Woman design, he was mostly talking about the New 52 long black pants making her design bottom-heavy which affects the reading of her figure a little differently than an all-blue Superman. But they both boil down to the same basic principles.Listen to Ep. 1359. Cliff Chiang makes the same comment when talking about WW's trunks.There’s a reason Superman (and so many other superheroes) had trunks on the outside of his costume that goes beyond the circus strongman visual reference, and beyond any issue of modesty, and that is that it helps the reader’s eye more easily identify the figure of Superman and what action he is performing. Because the red breaks the flow of the blue costume, we are more easily able to register the 2-D image in our minds, allowing the artists more flexibility in creating readable poses, especially in smaller panels. The trunks provide our brains with a visual cue. By removing the trunks from their heroes, DC has effectively hurt their ability to tell stories, albeit in a relatively minor way.
For some characters solid colors work great. I think Batman is a good example. He’s a character who is supposed to blend in with the darkness (except for the bat logo on his chest, which serves to draw fire to the heaviest protected part of his suit). With Batman, though, you can use the cape to express mood and action. You don’t have to rely on the actual figure drawing as much. In fact, you generally want his figure kind of hidden to add that air of mystery around him. Plus the ears of his cowl give him an easily recognizable silhouette.