"Arbitrary but standard" characterizes many English grammar "rules" and the way those rules used to be taught. Adding in qualifiers (hedging a statement--like "might" rather than "will"), which women often do in order to establish a bond with the audience by not seeming pushy or heavy handed (according to Deborah Tannen, if I remember correctly), was considered by "standard" usage guidelines to be apologetic and a sign of weakness. "Just give 'em the facts."