You're right b!x but I suspect that this isn't what they're used for.
I suspect that these figures are being used:
1) by the company to add to their allure to potential shareholders
2) by potential shareholders/brokers/etc to judge the allure of the companies shares
That is why, I suspect, they are measured against their *direct* competitors, rather than all other media types.
I mean, how would *you* react to an item that said: CNN had 647,000 viewers while Google had 2,928,844,236 hits - last month. ??
What would that mean to you, when you're trying to decide which cable company to invest in? Or even which industry? Would those numbers alone be of any use whatsoever?
I'm not decrying the substance of your point, I do think that the net has had and will have a vast influence on these matters, and the losses of telcos trying to become content providers are legendary and frighteningly large, but I think you've somehow sidestepped the purpose of such comparisons.