So, there's no specials in MotW.
And here I am, watching Supernatural for the umpteen time, and there's lots of sex. I mean, capital-l Lots. And it's relevant, too. Dean Winchester definitely classify for "get +1 and if you want, give +1 to your partner" special, or maybe the "it's not like it means anything" special. Sammy get his freak on less often, but it's still a couple time a season, and it counts likewise.
I started to think about the other source materials. Buffy ? A lot of people get some, and it's relevant. Angel ? Well, having (or not having) sex is actually a big deal for the titular character, and others get plot-relevant sex couple times a season too. X-Files is less sexually gratifying for their heroes, but damn, Fringe has a relevant sex scene in the first half of the first episode.
So, why not ?