I think it is more likely that they would reduce the size of creatures because of gameplay reasons, rather than for the sake of the miniatures line. The very fact that it was necessary to resort to terms like "gargantuan" shows that the existing size category system has problems. The complete inability of the size category system to function for vehicles and ships is another issue (albeit irrelevent for sizes of existing momsters).
As a whole, one can argue that for gameplay reasons monsters were just too large anyways. Shrinking a few of them doesn't seem to hurt anything if you ask me.