I hate this over-analyzation of "commuting" bikes. You can commute on any bike. I have a multispeed road bike and a fixed gear road bike and commuted all winter on the multispeeder (in -7 degree weather no less). Cheapie used road bikes (recent models, i mean) are less than $300 and usually have clearance for fenders or even *gasp* larger tires. I don't know about offroad but I ride over grass and dirt a lot on all these skinny tires.

Just don't downhill or anything stupid like that...