as others have said, it's ALL about time. if i could bike 50 miles in 45 minutes, i'd do it. if it took me over and hour to go 2 miles, i wouldn't do it.

my current commute is 15 miles one way, and time varies greatly by season and wind:

a dry summer day with a good tailwind on my road bike - 45 minutes (all-time personal best - 42 minutes))

a sloppy winter day with a bad headwind on my winter beast - 75 minutes

but most of my commutes average around 50 minutes on my road bike, 60 minutes on my winter bike. those times are a bit longer than i would ideally like them to be. 30-40 minutes would be much better from a "living the rest of my life" standpoint.