Sure, working people are not officially excluded from caucuses, but many times they either don't have the time, or would have to make an extra effort to get there. Plus, they'd have to be really interested to stay there.
Why would you think Obama spends so much time on college campuses? And why is so much of his support coming from those sources and not regular voters?
Caucuses are not democratic, which is why candidates selected by caucuses do so poorly in the general elections.