How is the massive infrastructure and programming cost paid?

I know a lot of companies pay piles of money to advertise on popular sites, but personally I almost never click on any of them (unless there is a button to make them go away) and rarely even remember what they were advertising.

Are there enough people unlike me to make all those advertising dollars worthwhile? Is there enough business/academic/government use of the Net for them to carry the load for the rest? Are ISP charges enough (and how much of those go towards general infrastructure as opposed to the ISP prinicpals?)? Am I overlooking something?

Or is the whole Internet a house of cards, waiting for a breath of fresh air to make it collapse?

(as a side note, I wonder if the whole of the IT world is the same. I've seen IT budgets in hospitals where I've worked go from almost nil to a very significant portion of the overall operating budgets - while in the same time, patient care quality has declined. Of course heath care, epecially socialized, is a lot different from general commerce. I'm sure the whole economy would collapse if all computers suddenly died, but not a lot of patients would die under the same circumstances, especially if all the IT people were transformed into trained medical personnel.) (rant off)