As far as I know all government machines are running FDCC(Federal Desktop Core Configuration) and the machines I've seen run IE7 with many IT departments recommending Firefox.
Fair - the town hall question referred to IE in general; it may very well be IE7 that they have at Foggy Bottom.
The FDCC only applies to XP and Vista. Additionally, there's no forced method to specifically upgrade those platforms to IE7 or above.
As does Britain's Ministry of Defence as well as many other departments in the British government. Moreover, they don't even have upgrade plans in place either.