When google made their first steps into advertising they took the view hitherto not taken too seriously. While the rest of the industry was using flash based animated adds, popups and even rather intrusive "pop-backs" (popups which appear when you close your browser windows), they eschewed those and went for POTA's (plain old text adds).
Their text based entry into advertising is discussed at How Google tamed ads on the wild, wild Web.
The article makes the point that while they were entering the market and sticking to text adds, some of the other advertisers were convinced that they would have to move to animated, flash based adverts eventually.
However, I would like to suggest that by going the text based route, restricting the text to a specific length, and make the adds context sensitive, google has succeeded in taking web advertising from a necessary evil, something you put up with, to a valuable and relevant part of an everyday web experience.
It is not suprise therefore that google is the only company which is making a lot of money from web based advertising. They saw the good in amongst the bad, they knew there was money to be made in web advertising, only if it's done right.
I find myself going to a web site now and getting severely irritated by "flash" (excuse the pun). A collection of horrible animated adverts that just plain make me mad. Those are the ones I want to turn off, they are the ones that distract me and make my browsing experience particularly unpleasant.
I much prefer going to a page which does not have animated or even picture based adverts.
Personally, I feel that google has been so successful at making text based ads fashionable that the consumer will start demanding that they are the only kind of ads that they see.