Knol and Wikipedia would be different in other ways. While Wikipedia is a not-for-profit and ad-free endeavor, Knol has a more commercial bent: Authors could choose to have Google place ads on their pages and would get part of the revenue.
“At some point, Google crosses the line, where they are not only a search engine, but also a content provider,” Mr. Sullivan said. Technically speaking, he said, authors, not Google, would create Knol pages. “But it matters how it appears,” he said. “I do a search on Google, I go to some place that Google hosts and I also find Google ads.”
I think this will come down, in part, to:
1. Information value and information value-add: if Knol has more useful and accurate entries than Wikipedia, people should go with the better source
2. Google's search heuristics: if there's any data suggesting Google is biasing search results to favor resources it controls, it should prove devastating to Google's "don't be evil" etc. good will, and people should search elsewhere