I apologize if there was some frustration coming through in the tone of my earlier comments. I want to keep this constructive.
True, while it isn't strictly necessary for implementing flexible images, leaving presentational attributes hard-coded in markup is far from ideal for a lot of RWD scenarios.
What I'm curious about is a filter hook that lets theme makers handle post format images in a manner similar to what already exists for other images in WordPress, rather than having to write another RegEx-style function to process the fully-formatted HTML string that's returned right now by functions like get_post_format_meta() and the_post_format_image(). This would ease development for those of us working on things like HiDPI image plugins, lazy loading techniques, picture element polyfills, and the like.
This hook could exist right now and I'm just missing it.