Good points by all. I think there are probably two issues. 1 is whether you will stick around. Companies spent a lot of time/ moeny/ resources training people. They don't want to hire someone who may up & leave someday to go on a bike ride.
2. Commuting to work. I would just say that I have dependabel transportation. The fact that they are even asking indicates that they know you bike to work (or else you are applying for jobs that require you to move about during the day, or they are low-wage jobs where people have a problem with dependable transportation.) I would not mention the bike commuting to anyone before I worked there. In a competitive job market, if you have two equally qualified potential employees, you are going to choose the safer bet. Biking to work may not be a problem. But then again it might. The new boss has no way of knowing how dependable you will be. Telling a complete stranger that you will be at work on time in a blizzard by riding your bike definitely rasises a questison mark. Once you have the job, you can show them you mean business, but beforehand, it's just your word that you will make it.
Anything that makes you the unsafe bet will cost you in the job market. Also, your co-workers might respect that you ride, but they aren't paying your salary.