Almost every worthwhile repo on Github has a README. A lot of them even use markdown. In terms of the source code, Github is for Git users--people that care about the code and commit history. Google Code isn't tied to a single VCS like Github, but it should still be developer-centric. After all, it's Google Code, not some app store.
Every time I get passed a github URL, it plonks me in a daunting page full of source code. If you scroll down a page or 2 sometimes you can see a text README file that tells you WTF the project is about.
On Google code, you get a nice UI, telling you about the project, bug tracker, discussions, binaries, AND IF YOU WANT IT the source code.
I think github is built for developers, whereas google code is built for developers and users.