I've confirmed the issue on my end; ?action=purge seems to have no effect and the 'last modified' notification on the mobile main page looks correct (though the content itself is out of date and not in sync with the 'last modified' notification). What's doubly weird to me is the 'Last modified' HTTP response headers says:
Last-Modified: Tue, 30 Apr 2013 00:17:32 GMT
Which appears to be newer than when the content I'm seeing on the main page was updated... Anyone from ops have an idea what might be going on?