I'm impressed too. I am 150xp from 19 on my DH and figured that was the top we'd see as I only used Tumble to move quickly from mob to mob with just enough to tumble back out if I needed to (rarely) and really pushed my fights hard. I'd say it has to do with the fact that I my main attacks showed up very early and are 75%, but hitting 4 enemies. Decent, but I could have cleared MUCH faster with some other abilities and better than a plain white 1h'r before Skeleton King (yes, that's right, I used a lvl 0 white weapon from lvl 3-Skeleton King. Insanity on drops)
Hardcore Diablo 1/2/3/4 & Retail/Classic WoW adventurer.