yes, I agree that's one way in which the roles are often different, but I think there's more to the contrast than that-
I am, after all, free a a citizen to engage in political advocacy (that's part of free speech), so there is an issue about the line between me saying things as Ulrike-the-scientist and Ulrike-the-citizen.
and, I guess what I'm arguing is that looking just at statements themselves isn't enough to distinguish these two roles