The House Next Door is on a roll lately. Today they're featuring an interview with Glenn Kenny, a film writer who edited the three articles that David Foster Wallace wrote for Premiere magazine.
Dave would often be commissioned to do pieces at 5,000-7,500 words so he understood that at a certain point in the process it was quite possible this would happen, but in a way he was constitutionally incapable of keeping to a word length. It was a tacit agreement you had with him when you commissioned a piece that you were going to get something long. But if you can run a piece that long, he's one of the cheapest first rate literary writers out there-you pay him X amount of dollars per word, but you get five times the words.
Kenny also wrote a short piece on his blog shortly after Wallace died.