I chose a road bike as my dedicated commuter for a few reasons, and I have not had a single regret / second thought.
1. Wanted to commute on a bike that I enjoyed riding above all else. Even after owning my Ridley for a month, I'll just stop and look at it at work sometimes and just smile. This is a bike that makes me happy just riding it to work.
2. I wanted to go fast. I pack as light as I can and pedal as fast as my lungs and muscles allow. I can't stand hopping back on my heavy mountain bike any more.
3. I wanted one new bike. Not two. I didn't want a commuter and a pleasure bike, that would be more expensive and take up more space. Instead I wanted a pleasure bike that I could make work as a commuter.
What I've done is bought accessories that make it a true commuter, but they are all quick and easy to remove. My
rear rack can be taken off in 15 seconds. My
headlight & mount comes off even quicker. Some days, especially if I'm skipping the gym and going straight to work, I'll just use a seatpost bag and no rack / commuter bag.
Riding in the rain is no issue. I don't get any mist from my front tire due to how little the water sticks to the thin slicks, and how wide my frames tubes are. The rear splashes a little but I have
a quick release fender that blocks all of it, or if I'm feeling lazy I can just use my rack + bag as a fender because that blocks mist. In an absolute downpour I ride my Trek 4300 with the fender and rain clothes.
After going this route I couldn't imagine doing it any other way. I fly past not just other commuters I see, but other bikers in general with my full rig.
I plan to use this exact same setup for my next cross country tour even, except I'm going to add a handlebar bag and mini panniers to the top tube.
This setup might not work for everyone but its what works for me. I want to pack light and GO FAST. I ride for pleasure just as much as I do utility, and nothing is as fun as speed.