Bretonia does, in fact, have an RP government. For example, I RP Prime Minister George Mountbatten. We've got a full set of cabinet ministers, and several Lords (and maybe an MP or two, but I'm not sure on that). Our in-game presence is minimal, of course, since the Prime Minister isn't going to be on the front lines. Our forum presence is a bit higher, but usually only when there's some RP that needs done with it.
Kusari and Rheinland both have RP'd leaders, as well, though I'm not sure either one extends to a full government.
I'd love to see the other houses get something like that rolling, though. Seeing a "West Wing"-like thread for the Liberty government would be cool.