The guy we always thought was Twitter's CEO now Twitter's CEOJack Dorsey, a programmer who's famous South of Market, is stepping down as Twitter's CEO. Why? Ev Williams, who's taking over, has a long, involved explanation about changing times and changing roles, and how Twitter was spun off from this loser podcasting startup he hated working on, and that's where he met Dorsey, who came up with the idea for Twitter as an in-house communications tool. Boring! What he really means:Williams is the guy who sold Blogger to Google. Everyone wants to hear from him, not some software engineer he hired. Dorsey is now "chairman," which is Valleyspeak for "founder we don't know what to do with."