I used to ride a "coaster" as a commute bike when I was in college. It works, but I rode flat urban streets. I wouldn't want to do it today.
I ride some massive hills on my commute, now, and prefer a road-ish bike for both it's sleekness and it's selectable gears.

For reasonably short commutes, though a coaster does the job. After all, when I was a kid I rode all over Hells half acre on a coaster bike and didn't know I was 'commuting.'
'Course, I wasn't trying to keep to a schedule back then.