I commute and do all my riding on my fixed except during the winter. It works for me. While these bikes lack racks and all that stuff, they're well suited to moving quickly through heavy traffic, short bursts of acceleration, and having fun while doing it. I just throw all my stuff into my backpack which can occasionally weigh upwards of 25 pounds since I like keeping weight off the bike.
For some people it wouldn't be ideal, for others it is. Courriers basically started the whole urban track bike thing because they felt it practical for their purposes. Other people ride in on touring frames with panniers, full fenders and steady as she goes geometry because that's what works for them.
It's like comparing commuting in a Porsche vs a minivan. Both work, one is a lot more fun, one is slightly more practical.