I live in one of the largest and most bike aware places. It is still just a numbers game and luck. It certainly will cut my life short as is and disability sucks, but I still ride. No one can predict someone pulling directly into a passing car from a parallel parking spot. That level of stupid is beyond belief, but it does exist, and it got me riding to work 2/26/14
For lifting weights it's confirmed that your prolong your life by more than what you spend in the gym, i think for 30-45 min sessions, which is enough.
Not to mention the saved fuel cost, car maintenance cost and/or public transport cost ( though the latter is often reimbursed by the employer as well ).
You do get some money for driving to work in your taxes IIRC, but not even close to what you spend.
In my own personal experience of doing it in London for years (nowadays I'm in a different country and just walk to work) as well as a conference I attended way back by a researcher studying exposure to polution in London, if you're doing it in a big city like that, try and find a path that minimizes your exposure to polution, since whilst you actually get a proper daily fill of exercise cycling to work, you're subject to the same risks as people who jog near roads with lots of traffic, which include such unexpected things as a higher risk of heart attack (due to soot microparticles from ICE exhaust transversing the lungs into the blood and ending up accumulating around the heart) as a well as (more expected) problems in the respiratory system because the sulfur oxides emitted by cars (especially diesel) mix with the water in your airways and lungs and turn into acid.
Mind you, it doesn't need to be that much of a detour: from models I've seen for London polution, merely being one street over from a main road massivelly decreases the polution levels one is exposed to.