I have two "commuter" bikes and they differ quite a lot. One of them is a cheap aluiminum cross frame with 105, cheap wheels, massive tyres and serious mudguards. I use this one to and from work and for my workouts on the road in bad conditions.
The other one is an old Trek mtb with a rusty suspension fork and with a 50% chance a gearshift won't happen unless i click the lever twice.
The cross/road hybrid never gets parked in a place where a lock is needed. I try to bring it inside or lock it away in a shed or similar when i ride it. It's more like my second roadbike but and my commute is 30 k so it reguired suiting up in full cycling gear. The Trek is my beloved "gettingaroundtown" bike and i have no second thoughts locking it away for a weekend in a "shady" place.
I find it interesting what certain people refers to as commuting. If i ride from my apartment to the city center i wouldn't call that a commute as much as a ride into the city. Same goes for riding to my girlfriend or even my mothers house which are located about 4-8 k's away. These rides aren't commutes in my view, but rather a necessary thing because i don't want to pay for the bus or have a car.
Commuting for me is a daily routine which involves getting geared up and sometimes requires a "special" bike. Spare clothes is needed as well because the ride will certainly make you sweat. I don't know how other people define the word commuting but it could be an interesting discussion. Sorry for going off topic by the way, i just can't wait for a dedicated commuting section