This is not quite correct. If all you want to do is checkout the source locally and start exploring it, github also supports Subversion clients. Simply grab the HTTP URL from the github repository page and use that as your URL in the File | Open from Version Control dialog:
You can also browse the repository and look at file history and file diffs using the VersionInsight IDE tools.
I haven’t gone too far with this, so not sure exactly how compatible the github SVN support is, but so far the read-only scenarios I’ve tried all seem to work.
I should also put in a plug for Uwe’s VersionInsight Plus, which is rolling first class git support into VersionInsight (along with a lot of other cool stuff). If you’re looking at git for anything beyond simply browsing other people’s sample code, I’d strongly recommend you explore this.