There is lot of hype around wikipedia especially in the context of wikipedia versus knol that blog were given a bad name. That is only a blog has become a derogatory sentence.
Many blogs are extremely useful not because they are diaries but because they were websites easily set up using blog platforms. Blog is now promoted as easy website and not a pesonal diary.
It is interesting to note that blogger is ahead on wikipedia in terms of popularity as per Alexa ranking. But statistics about blogger platform are not available as compared to wikipedia and many people may not know the popularity of specific blog posts.
If blogger is successful why knol will not be successful? Under normal logic knol will be succesful.
But will knol cannibalize blogger? Will knol get different types of persons as authors and different types persons as visitors and improve the performance of google? Still all over the world more and more houses are getting internet connections and market size may be expanding and that may go in the favor of knol like platforms. Knol may turnout to be big learning platform maintained by a number of individual authors competing with each other for visitors. The innovative, consumber savvy, and tenacious persons only will grow to become more enduring authors.
Regarding success of knol, I do not think there needs to be a logical doubt.