1st position in Google gets around 90% of all traffic in some cases...It does depend grateful on the term you target etc, I would use a better curious description. Trust me, I am in offline marketing, I know what I am talking about.
That happened to me as well. In my opinion the search volume that GKT shows is way exaggerated. Now I always compare the results with http://tools.seobook.com/keyword-tools/seobook/ to get an idea about the traffic.