Your belief that selling ads is not valid or useful to the user never ceases to amaze me.
You sell a few online webapps, and get a full cut.
People showing ads, sell them tech, finance, cars, whatever. Anything that's relevant, and get a smaller cut.
A smaller cut of a massive pie is often better than a full cut of a very small pie.
The website selling directly has a finite (small) number of things they can sell the user. 37signals can sell me a basecamp subscription, a campfire subscription...
The website advertising to the user has a massive inventory they can get the user to buy. Each time the user comes back, there's another chance to sell something new to them.
I'm guessing either you tried advertising at some point and couldn't get it to work for you, or you just hold some sort of weird grudge against advertising and see it as evil.