backdraft7 - 2:51 pm on Sep 11, 2012 (gmt 0)
I'd say it boils down to more competition. As a simplified example: If there were 10 sites in your niche in 2003, they would typically divide up the traffic between them. In 2012, there could be 50 or more competitors in your niche and Google now appears to magically cycle them all to give equal share, which assuming traffic stayed pretty much the same or even increased, would amount to a net loss for everyone. All depends on your niche.