Responsive Web Design is a watershed in the web development world. You build one website for your business that serves a variety of different devices. It is the logical culmination of accessible, semantic web design.
The issue is the sheer range of devices: laptops, PCs, tablets, mobiles, mobiles that think they’re tablets etcetera and so forth. To cater individually for all these devices would take an age, so the team simplified the whole landscape into “HTML4 browsers” and “HTML5 browsers”.
What I find really interesting is the focus on speed ie reducing file sizes and the number of requests for files made to the web server. When I were a lad, we had to keep the entire page to below 30KB, images an’ all. Now, wildly differeing data connection speeds demand the same rigour.
But, what the hell, to hell with bad browsers ;)