Moderators can update the headline and link; fixing in place can be better than another submission on the same topic, because it aggregates upvotes and conversation in a single place.
Given how rarely it happens (though it does happen) and the volume of links, I suspect there just aren't enough moderators. It might therefore be more ideal to give the community the tools to enforce.
Okay, so why not have something that submits "better link and headline" and that can be voted up? Pass a threshold and the original headline and link get swapped out.