I would argue that commuter bike does count as a genre, or at least a sub-genre, as many manufacturers split their "road bikes" from the much more relaxed ones targeted at commuters. See, for example, how Cannondale has a "road" section and a "recreation" section, which contains bikes with flat bars and marketing images of people riding around bustling cities rather than racing or doing hardcore fitness rides. Jamis splits out "road" and "street" bikes, and "street" even contains a model named "Commuter". Kona splits out "road" and "asphalt".

Further, if I bought, say, a Kona Smoke, rode it only on streets, and came here and posted it with a thread titled: "Look at my sweet new road bike!", I would rightly get laughed at. Therefor, I would contend that for a bike to be called a "road bike" it should at least very closely follow the template of a racing bike, if not necessarily conforming in quite every way.