I think most workers factor in the commute when they are looking for and choosing a job (I know I do). Now, we can argue that workers undervalue the time and money they spend commuting, but it is still not 'free' for the employer.
Also, not all of the commute cost is the fault of the employer. For example, my commute is a lot shorter than many of my coworkers, because I place more importance on a short commute than a cheaper, bigger house further away. My coworkers value having a bigger house more, so they live where the housing is cheaper but the commute longer.
How would your price this in? Would the people who commute further get to work shorter hours, just because I chose to sacrifice for a closer commute?
I think a fairer deal would be if commute time counted against the typical 8 hours of work. That way everybody's interests would align around having short commute times.