I think if you air a show on HBO there must be some sort of minimum requirement for sex scenes and so much nudity... I guess they assume that audiences paying for it expect it and want to view such stuff (Showtime is just the same- I can't even watch a whole episode of the Tudors)
Sex in cinema has always bothered me- who in world wants to sit with family and friends while watching actors simulate sex? Okay- well maybe, some people do. But I always find it awkward, embarassing even... I have two big brothers for the love of God and it's damn uncomfortable sitting through a sex scene with them. (and we gathered together every sunday night to watch this series)
I think Rome would've been just as enjoyable had they left the graphic sex stuff out. And as far as I can tell most of it just steals valuable time from the characters' dialogue and historical content of the show...