mona - 7:14 pm on Mar 23, 2005 (gmt 0)
Advertising on the SERPs gives them until now the most revenue, but when searchers massively go to other search engines as happened a few times in the past Google's biggest source of income will dry up in just a few months. AdSense is a way for them to diversify their income sources, even if their search engine becomes less popular. Just from a survival point of view they cannot ban too many publishers sites from the AdSense network without reason. These sites may be their only income in the near future.
Interesting take, lammert. I've never thought about it, but I'm sure the boys over at the 'Plex have. This could certainly be one of the reasons they allow scrapers and other poor quality sites to advertise.