Fortunately due to advances in mobile technology this could be a thing of the past in the near future, back before 3G there was a real need for low-bandwidth sites and hence mobile specific versions of the site.
Now we have devices with larger screens, faster processors (which often now include GPUs almost as standard) and proper browsers that support much of what their desktop equivalents do.
Give it a few years and hopefully more web developers will see the importance of flexible design for their webpages, that is if the App craze doesn't kill this off.