Pete,
You are listed as having over 2000 posts on a bike forum and you are asking us why we commute on a bike?? I don't get it. Are you asking a rhetorical question, or are you against commuting, or what? Maybe you know the answer and you want to see what people will say about it. Seems like a strange question to me, but I will answer it anyway. The pollution I save by riding my bike is a mere drop in the ocean. Besides the obvious health benefits, I ride because I enjoy it and because I am doing something that 95% of americans can't, won't or don't. In my own way I am showing people that I am an individual, and that I don't necessarily follow the herd all of the time.
Sometimes a cigar is just a cigar, know what I mean?

-BT