[0] => No ads and it is clean. It is made by people who don't intend to make money, created by people whose world don't revolve around money and read by people who value knowledge more than money.
[1] => Wikipedia is millions of pages ahead of Google Knol when it comes to content. 7 million pages in 200 languages. Money can't buy you that.
[2] => Wikipedia is synonymous with knowledge but with Google Knol, only the first four letters match, that is the closest it comes to knowledge.
I can go on, but will stop here. This is Google's narrow minded way of making money by showing more ads. They clearly were directing lot of traffic to Wikipedia pages, they realized why direct the traffic to some other site when we can let users steal content from Wikipedia and show it in Knol.