A few guys deserve some credit here.
Voeckler is obviously the most successful attacker this year, he's been doing very well and that's probably why he ranks so highly. He's perfected his game this year and clearly has killer shape. I don't think he's the most aggressive though.
Gilbert is the strongest attacker in the peloton. You've got his last k attacks, his Poggio, Bosberg, Roche aux Faucons-attacks and of course his massive success rate. Gilbert is too strong to be a real attacker though, that's why we only see him in the final of a race. His success has made him less aggressive and more calculated, but he's still among the most aggressive riders around. His performances the last weeks were soaked in aggression.
De Gendt is currently the best guy for the long attacks. He attacks a lot, has a nose for the right breakaways and measures his efforts perfectly. He potentially has a very big career ahead of him with a lot of fans. Wouldn't call him the most aggressive though.
Vino can be considered the most aggressive rider of the bunch, but this year isn't his strongest year. He's still one of the best riders around, but his age surely does affect his aggression score. Probably still the most aggressive guy in his head, but not in reality.
Hoogerland is very aggressive and mostly crazy, that's why I award him with a second place. Not sure what happened to him after 2009 though, he looked a lot stronger then.
Txurruka definitely belongs on here as well!
Bakelants, for me, has been the most aggressive rider in the peloton the last few months. He's been in countless breaks, has attacked on so many occasions and has done all this without taking one win. Seemingly not bothered by this he kept attacking in the TdS even though his shape wasn't perfect anymore.
The rest, nah.