I'm one of those who says any bike will do for commuting.
Every time there's a transit strike somewhere, the news has pictures of grown men riding their daughters' Barbie bikes to work--white tires, streamers and all.
Is it optimal? No. Is it doable? Evidently.
“Commuter” as an adjective is not descriptive of the object, or its features, but rather, what is done with the object or who uses the object.
Commuter trains are used by commuters. Commuter towns are where commuters live. Commuter colleges are those that people travel to daily.
None of these usages describe the nature of the train, the nature of the town, or the nature of the college. It's only in the fantasy land of bicycle marketing that commuter describes a set of functions and features an object possesses.
In other words, in the real world, there is no such thing as a commuter bike. But there are commuters who use bikes.
In marketing terms, my 1996 Litespeed Classic is a racing bike based on “classic” Italian road bike geometry. It has no luggage rack or fenders, nor provisions for them. Yet, twice a week, it's a commuter bike. Nothing about the bicycle itself changes, (Okay, this time of year I put lights on it.) only its destination when I ride it.
My 2006 Trek Portland was marketed as a high-speed commuter. The rider makes the bike fast or slow, so there's that marketing term out the window. It has features that many commuters find desirable—rack and fender mounts—yet those same features are desired just as often by touring riders. I've ridden it on centuries, and to the to top of Mt Evans, 14,130 feet. Hardly a commute.
However, most people would instantly recognize the Portland as a “road” bike. The drop bars and forward-leaning position are the dead giveaway.
My 2013 Ribble Winter/Audax is marketed as a winter training bike. I don't ride it far enough for an audax (AKA brevet, randonee), and thus far, I've ridden it in every season but winter. Its drop bars and rider position also make most people call it a road bike. But I've slapped a rack and fenders on it and ride it to work when I need to tote stuff, or if the chance of rain is between 30 and 50%.
Why roadies? Because that what I like. Roadies make me happy.
I work on average 216 workdays a year. The last workday I didn't bike commute was in July 2006. (To save you the math, tomorrow will be the 1,552nd consecutive workday of bike commuting.) So I take little stock in those who say road bikes aren't tough enough, or that you must use a Dutch bike to commute, or an MTB, or an IGH, or 32-spoke wheels, or anything else. Baloney.
All that matters is your destination, and then any bike you're on is a commuter bike. With luck, your bike's style and feature set will make you just as happy with yours as I am with mine.
And you can call it whatever you like.