Pros and cons of cycling to work and back 5 days a week?

Balls. It's better than fuck all exercise (sitting on the tube) and if you push yourself it's a good 50mins-1hr of exercise everyday.

How can that not make a difference?

Fair point. Then again, everyone is different in make up. What works for one may not work for another. Just because i remain a fat bastard does not mean others doing the same distance wont reap the rewards.