PokerEV graph question

http://i171.photobucket.com/albums/u...2-27--0-18.jpg
What are possible causes for such a consistent disparity between sklansky bucks and showdown winnings, with the sklansky line always being higher?
And any general interpretations of/comments on the graph are welcome as well.

it could be that youre running slighly bad or it could be that you give up on too many pots too early and arent aggro enough with draws, etc.