This is just my take.

My commute to work one way is 18 miles. I have been racing for the last 3 years and have pretty much abandoned commuting and replaced the ~2 hrs with time on the trainer. I haven't ridden to work in 6 months.

It's hard for me to replicate any benificial adaptations needed for racing while commuting. The trainer allows for more specific workouts. VO2 max, 2x20's, - I also have a few workout dvds.

That said, I enjoyed commuting but found it did little to improve my racing prformance. I have no natural talent so, again, ymmv.