The WGA (writers guild of america) has the whole
article online now.
Ironically, out of the 6 episodes he wrote (1ACV06 - A Fishful of Dollars, 2ACV01 - I Secon That Emotion, 2ACV10 - A Clone of My Own, 2ACV15 - The Problem with Popplers, 3ACV08 - That's Lobstertainment!, 3ACV16 - A Leela of Her Own) at least two belong to my least favourite episodes (clone, lobstertainment) and one to my more favourite ones (popplers).
That said, the award was not only for his writing on Futurama but for his lifetime achievement for animation, so things like him being treasurer for the WGAw probably play a role, too.