Of course the Web is free, for the average user. But Richard Stallman wants to make it more explicit for the Web. Just the other day some of us were trying to apply the open source philosophy to the Web technologies. When the Web was born, all the source code (it was only markup and style then) was open and accessible by default. However, with time, more and more technologies have been able to power Web, and consequently hide under it. Most of the everyday users interact with only the Web interface, they never really have to deal with the underlying technologies if it works. In fact, it is not easy to get the information even if someone wants it.
This must have received criticism from some who think that this is getting too puristic to be pragmatic. However, I do not think this can be enforced on anyone. It is a matter of ideology and if you are the one who follow FOSS, then you will like this. It will encourage use and growth of FOSS philosophy. However calling the browser vendors to support this might run into stalemates. It might be quicker to see if we can build plugins/extensions/addons for them that give out warnings about web sites with proprietary code.