I think they're using Git. But this would clearly be awesome... (And an alternative to full github access).
One easy way to do this would be to create a public repo sencha-touch-nightly on your github, and then with a daily Cron -> git pull YourCurrentRepoOrigin --force ;git push ThePublicRepoRemote --force.
Oh pleaaaase ! I'm stuck on PR-1 like... Forever !!!