Are they really too big? The comparison shot shows that they're about a head taller than the GW figs, so about 8-10" taller in scale. I'm pretty average height and have plenty of friends who fall within that range either taller or smaller. Real people tend to be way more variable in size than minis ranges are.
The mugs are more noticeably different, but maybe GW's barkeep is just a stingy SOB. Could even do a scenario around two competing taverns feuding over prices and cheating by offering smaller servings...