Interesting how occasionally a guy below the top 5 or top 10 is able to do well with the #1 on a ladder, but this has happened before in tennis. It's true that Davydenko beat Nadal in Qatar the other day, but unfortunately for Davydenko, Rafa was sick with some kind of flu bug. Then, a day later, Nikolay had to play Federer. Roger won in straight sets.
http://www.atpworldtour.com/News/Tennis/2011/01/1/Doha-Friday-Davydenko-Hitting-Form.aspx
http://www.atpworldtour.com/News/Tennis/2011/01/1/Doha-Saturday-Federer-Reclaims-Crown.aspx
You're right about the head to head record: Davydenko has 6 wins to Nadal's 4 wins.
http://www.atpworldtour.com/Players/Head-To-Head.aspx?pId=D402&oId=N409
If we look at the top 100 players currently ranked by ATP, we see that Nadal is #1 with 12,390 points, while Davydenko is #23 with 1,555 points.
http://www.atpworldtour.com/Rankings/Singles.aspx