If you haven't seen C. Enrique Ortiz's page on mobile context, you really should do so, especially if you are a designer or developer.
User and device context is the key differentiator between computer-based applications and mobile-based applications. What is the user doing? Where is the user? Is the user available or not? Which device is the user using? Who is nearby? Is the space quiet or noisy?
Sure, we can develop devices that render "the one web" adequately while mobile. And sure, for the majority of sites this will be the best answer. But there is a large number of sites - most anybody with a user experience team, for example - that need to consider the mobile context.
My best evidence that there will be a mobile web is the ever growing number of sites targeted just at the iPhone. Here is a device with the best current web rendering available, that even pushes the boundaries. Nevertheless, developers and users seem to want a contextualized user experience.