I hate it when people confuse "mature and adult" with "gratuitous sex and gore." I love me a truly mature game, but maturity does not come with boobs and sensationalist sex scenes (or sex implications; the poll offers the laughable examples of Dragon Age's and Mass Effect's so-called sex scenes). As a matter of fact, it has the very opposite effect; they instead end up appearing very juvenile and immature. The moment a game decides to flaunt a naked boob (what about naked men, by the way? One thing I've campaigned for in the past, when it comes to The Witcher 2, is that there should also be male nudity in the game. Fair is fair, after all.) or playback a sex scene, and does so in a way that makes it apparent that they're doing it just for the sake of it, they lose a whole lot of credibility. (The same goes for blood and gore, of course, but this topic seems to be focused on sex.)
A mature game stands neutral in relation to sex and nudity, which means it neither sensationalises it nor censor it. It shows the "reality" of it if it fits the world it takes place in, in a way that makes the player notice it, but without making them get stuck in it. A mature game can portray these things either in a "gritty and real" way, or in a "romanticised" way, if it chooses to; it really doesn't matter, as long as it feels like it belongs, and like it isn't there for simple shock and awe (or to make drooling boys soil their underwear). The Witcher 2 has already been mentioned, and that by all means is a mature game, but for other reasons than nudity and sex (which it sometimes succeeds in, and other times is guilty of the gratuity factor). It is a mature game because it deals in issues that matter and feel real, while it at the same time paints us a world riddled with characters and events that are believable and make you think. I digress...
The poll made me roll my eyes. It focuses entirely on female nudity, and none of the options anywhere felt satisfying to me. I ended up voting "no" everywhere. Project Eternity could have nudity and sex in it, sure, but it needs to be done right, with none of the sexism or gratuity or the censored PG13-dito Bioware gives us, or not done at all.