Yes, this is sometimes the problem. Also sometimes you have to select the format or you may not get the resolution you want. One of my webcams generated 300+ different video formats and the default one was NOT what I wanted (very low res). So in the end you want to enumerate video devices like you are doing and set the right track/format.
Sometimes though, the capture device just plain does not work even though it shows up in the media player menus. All you get is black and there are usually no tracks/formats available when you enumerate them.