Is biking 10 miles a day enough?

Excuse me, I was just reading this passage about biking and it mentioned someone biking 10 miles a day. I'm curious, as a fitness enthusiast, do you think that's a sufficient amount of exercise to maintain good health? Is there a specific reason why 10 miles was chosen as the example, or is it just a general guideline? I'm trying to set some goals for myself and want to make sure I'm on the right track.