Four Candidates?

Today, I watched the debate between Obama and McCain. The debate was held last month too. Everyday media features the two candidates. These situation made me think that there were only two candidates in the presidential election. However, a friend had a piece of paper for absentee ballot today, and I found that there were four presidential candidates in reality. I know only the two have a chance to win in actuality. However, is it fair to give chances to debate on TV only to the two?