Sure Julia Gillard, Obama, Sarkozy and that British PM would love have top Mercedes as their daily ride but have the same problem of explanation of foreign vs. domestic choice to own electorate.
Willy Brandt did not have that dilemma, same as the most (self)elected presidents of countries that do not produce luxury limo's.
but after reading on Wikipedia that even Jeremy Clarkson own(ed) one, I sure now believe that 600 IS a dictators car (what would Jeremy be like president or PM?)