I regularly commute on a Jamis Aurora, a sport touring bike, that I purchased for weekend rides and touring. I intended to continue commuting on my Trek 7300 FX when I purchased the Aurora, but I quickly found that I like the ride of the Aurora much better, it was more comfortable, the gearing was better, basically, I wanted to ride it more! The 7300 FX went into storage.
Earlier this week, I broke a spoke on the rear wheel of the aurora. I took the 7300 FX out of storage, cleaned it up a bit, transferred the lights and necessary bits and rode it to work yesterday. To put it mildly, I did not enjoy the ride. Rather than enjoying myself on the ride home, I spent much of the ride trying to figure out how much I could get for it on Craigslist.
I suppose my point is, find a bike you enjoy riding. If you ride it to work, grocery shopping, time trialing or CX and you're enjoying yourself, then it's the right bike. I'm not an N+1 guy, but I do have more than 1, and I hope to soon decrease that number by 1.
All that said, a lot of factors can change things... distance, security, season, location etc all contribute to determining which bike may be appropriate for your commute.