I just want to comment on the difference between Japanese games and Western games re: porn vs drama with sex. At least here in America, we are way more prudish about sex in media than Japan. In America, if your product contains graphic depictions of sex, there is a high likelihood that it will be classified as porn, and therefore not be taken seriously. In Japan, a serious RPG that has sex scenes would not be cast aside in that same way. Thus, in America, people are probably more reluctant to "just add some sex to sell my otherwise serious game." With few exceptions, things are seen as either porn or not porn, and people (as in "the public") don't generally expect much from porn.
Some of the better devs in this little sub-industry are defying that paradigm, but they aren't exactly getting reviewed by IGN or invited to E3. They are still seen as porn by the general public. Compare this to the challenge of leaving a career in porn to become a mainstream actor/actress. It's happened, but not often. People who want to become serious game developers with public appeal are not going to just throw some porn in there to get sales, because that may well relegate them to being seen as pornographers.
Additional comment: If Rumiko Takahashi wanted to do a hard-core hentai comic for a couple of years, and then wanted to go back to light-lighted comedies, I doubt anyone in Japan would think anything of it. You can't do that in the U.S.