I use grease in any metal to metal connection, if you torque the bolts up to the correct torque then most of the grease will be squeezed out leaving just a very thin film, this won't allow the bars to spin around at the correct torque.
I think most folk have heard of seat post frame seize up, just because it's something thats adjusted more often, and the fit bewteen the post and tube is (normally) close, so galvanic corrosion occurs easier, also the loaction of the seatpost means that more water gets in there, so if its a steel frame that accelerates rust .