Our sister-site WoW Insider did a bit of digging to find out why Blizzard jumped so much in a single year. It seems to be due to a few things combined; Blizzard's Activision merger, the release of Wrath of the Lich King, and a change in the way Develop is calculating their figures, particularly in relation to MMOs. Here's a summary of the judging standards found on the Develop 100 page:
Develop 100 ranks the world's most bankable games development studios based on a variety of key criteria including sales data, critical success and industry standing.
Things get a bit wonky when it comes to sales data and MMOs, due to significant revenue coming from subscriptions and online purchases instead of retail sales. WotLK's release and resulting retail sales undoubtedly had a great deal to do with Blizzard's new number one standing, and we wonder how old Blizz' would have fared on the Develop 100 without a new box to put on store shelves. Regardless, they're the champions for 2009. For those interested, the top 5 in order are: Blizzard Entertainment, Nintendo, Rockstar North, EA Canada, and Capcom.