I don't disagree that it can already be done... your doing it, I'm doing it, many are doing it via CSS media queries. But the ultimate in responsive design is to limit media queries and deliver the lightest page as possible to a mobile user with the least code possible. That is the ultimate in mobile design, and still one reason why many sites make a choice between two sites, i.e. m.site.com & site.com, or responsive.
Responsive is still code bloated, and that is the major setback with responsive. It's advantages outweigh the disadvantages, no argument from me with that one.
I'm purely saying the ultimate in mobile design is to have the ability at template rendering to add or remove code entirely, not hide or display relevant elements, like we do now.
Not sure what the IE is about... as I didn't mention anything about that. Obviously that was in response to someone else?