I agree and desagree.
My theme generally manages responsive images as you describe above.
But it doesn't manage content provided by users (news or pages content). As example, personnal content may set width or eight on images, that breaks responsive behavior.
So, with my theme, each image should have 2 classes : `img-responsive` (class to be responsive, with the same css rules than yours) and `remove-attributes` (for jquery cleaning of unnecessary and unwanted attributes).
Of course, gallery content automatically add these classes, but they should be added manually for each personnal content that user want to be responsive (my theme doesn't know if user want its content to be responsive or not).
So, with these 2 classes, my theme is robust, with pictures managed by zenphoto (thumbnails and other sized pictures) and pictures added by users in news/pages contents.