Hmmm ... I guess erections got covered because men with erectile dysfunction, instead of whining and fibbing like a two-year-old at a Nancy Pelosi dog-and-pony-show, apparently went directly to the marketplace and made it well-known that they wanted such medication included in their policies, eh?
Of course, another reason might very well be that Viagra, et. al., are used to restore proper function to a currently dysfunctional part of the body and birth control pills are used to prevent the body from functioning in its normal manner.