Why was Joe the Plumber not invited?

The final US presidential debate has just concluded, and from what I can see on the web, McCain did not get the knockout blow he needed. That butt-kickin’ just didn’t happen.

Anyway – if anyone watched it or has comments put them in here. From some comments on the midweek thread, it seems like a plumber called Joe was more involved in the debate than any other plumber. And that’s gotta be good for his business.