Exactly as above in my eyes. I have a ridiculously short 7km commute and jsut use my winter bike with bottom grade Campag and 23mm Gp4000s. For commuting I really don't see the need for fancy parts or equipment or a special bike. just ride a cheap basic road bike.
IMO, you need a more road-ish commuter the longer your commute is. If I had a short commute and trips around town, I'd use a pretty upright bike with full fenders, lights and rack all the time. The longer the commute, the more likely the comfort and utility compromises become worth it for the efficiency gains.
My commute is 23 miles each way, and I ride a full on road bike, and shower at work - but we rarely get rain, and the clip on fenders work well enough.
That being said, my experience with my commute over the last few years would make having a cyclecross bike with fender and light mounts ideal...possibly with a disc brake setup for rain / trail use. I'd also run some tubeless tires with sealant on some sturdy rims to deal with pinhole flats.