aristotle - 2:56 pm on Apr 3, 2011 (gmt 0)
Surely everyone realizes that most existing webpages are low quality. Less than 1% are what I would call high quality. Thus 99%+ are low or mediocre quality. This means that for millions of search terms there simply isn't any high quality information available on the web. That's the basic reason why you see so many low quality pages at the top of the SERPs.
The web in its present form is only about 20 years old. There are still big gaps where nobody has created any high quality information. It needs more time to develop.