Confirmed that getting my voice overlaid with the game sound track is going to be difficult with a USB microphone. That is really unfortunate. They should require a warning sticker on all USB microphones: Warning! Your style is about to be seriously crippled by this piece of dog squeeze.
Possible solutions include recording the game session and mixing my voice in later. My son says he likes to make videos that way because he can think about exactly what he wants to say and do retakes if necessary. I'm a spontaneity type guy and although I will do that if forced, would rather have an authentic video where everything happens real time.
I'm looking at some other alternatives and all I can find is paid programs, when I'm spoiled by Linux to think that great software should be available for free. After all, I paid extra to get a Microsoft LifeChat 3000, only to find that in order to use it I have to spend that much again for software? Makes me cranky just thinking about it.
So the search continues for free software that will take the USB microphone feed and repeat it into the stereo mix. Google is gonna earn its money today!