There is a very interesting presentation at http://www.slideshare.net/yiibu/adaptation-why-responsive-design-actually-begins-on-the-server . It covers the challenges in responsive mobile site creation, and proposes a hybrid solution of device profiles to solve it.
The first half of the presentation is worth showing anyone who does not understand the challenge of developing a mobile website that works well on multiple mobile devices, not just on the latest and greatest iPhone / Samsung / HTC.
Added to this is that the word ‘smartphone’ retains a nebulous definition, and in fact today’s ‘cheap’ devices contain most of the features that a smartphone has (e.g. touch screen, browser), however their ability to serve the web may not be as perfect as Apple’s Mobile Safari.
This is the reason that content adaptation has had a number of solutions, via examples such responsive design, server-side detection and adaption, etc.
There are also some interesting suggestions at the end of the presentation about some potential options for the future, e.g. changing the <img> from having one source file to having multiple source files (similar to the way the <video> tag is currently done). I would be interested in this option, however the reality is that the HTML change process is long and tortuous and thus I won’t be holding my breath.