Not that I'm going to argue that the cost of a TV is not worth factoring, but I think the reason that most analysis leaves the cost of a TV out of the cost of a console, is because the assumption is that people have TVs anyway. And people will buy HDTVs without consoles. One might argue that consoles push the adoption of HDTVs, but it's not a 1-to-1 relationship.
As a single datapoint, I have a giant HDTV, and I don't have an HD console yet. *shockhorror*
You can argue the same bits about a PC, that you can have a PC and not game, so the whole cost of the PC isn't relevant. Certainly true. So, let's compare the cost difference between a PC for average use (not computer specialist, not graphics artist, without those outliers) and the cost of a PC for gaming use. Then compare the cost of a TV without a console, and a TV with a console. Careful though, that way lies relevance, rationality, and inevitably, insanity.