^ The abs always looked silly to me in the comics too, so that doesn't really justify it here. For Superman and Spider-Man, you don't really think much of it because they're huge exaggerations of characters and they're so powerful they don't need to protect themselves. (Although, both of them were handled with a lot of tact in their most recent movies, I thought. The musculature isn't overdone.)
With Batman though? It's typically more down to Earth. They want you to feel like he's just a man who needs a suit that protects him. But even though there's a mesh underneath his clothes in the comics, he still just looks like he's a naked bodybuilder covered in grey spraypaint, and it's ridiculous.
Some artists take it easy on the definition and try for a more subtle approach, while other artists are just abstract enough that you can shrug the rippling abs off as an artsy expression of strength that isn't meant to be taken super literally or be seen as realistic (no fabric hugs THAT much).
When you adapt Batman into a live action movie, it's got to feel believable in a real life situation. I know he's still armored as a geeky fan, but it's not illustrated well visually, and the bulging muscles still come off as over the top and cheesy. His anatomy is pushing through the costume so much that it really is amazing that we don't have Bat-Nipples again.