Just curious: why not ride a regular bike to work? I've been doing it for a year now (16.5 miles round trip) and it has been great. I never could find the time to exercise before and now I commute and exercise at the same time. Parallelism!
I do have a non-cheater bike as well, I ride it more when it's cooler (but I'm still lazy, so...) More exercise is the plan. Executing on that plan isn't always successful.
Of course, several years ago after I decided to get in shape, I tried cycle commuting and really enjoyed it (about 15 miles each way). But I could only pull it off about once a week or so (in order to make good time, it left me mostly worthless at work all day). Coming up, after I move in a month I'll be about 23 miles from work. Adding a hub motor will allow me to not only make the commute in just over an hour, but it will leave me less exhausted (I plan on still putting in some human power, but I won't have to over do it). The good thing though, is by adding electric power to a bicycle, it will get me on it much more often so I'll end up getting even more exercise than without power.
Maybe someday I will be in good enough shape to make the 20 mile commute in around 1:15 without the assistance, but if it's between pedal assist and driving, pedal assist seems like the far better choice!
FWIW, I used to bike-commute to school when it was 8-10 miles, and that was great. But 20mi each way is just too much time for me when I need to get home to get kids to practice, or help with homework, etc.