The Entertainment Software Rating Board, or ESRB, will be old enough to drink alcohol in the United States this year as it celebrates its 21st birthday, having been introduced in 1994. Despite that, there are just 30 or so games with the ultra rare Adults Only rating. Among those few are a cancelled game, one that was only rated AO long enough to get the game a re-release, and a couple PC-only directors cuts.

To release a big game with an AO rating is essentially sending it off to die at retail, so it's not surprising that it's so rare. But in the world of digital games, what's stopping publishers from adding AO games and editions of games to their rosters?

A small publishing house called MangaGamer that specializes in localizing and importing Japanese visual novel games can enlighten us a bit on the subject. While MangaGamer has about 15 games in the All Ages section of its website – I'll let you punch their name into your search engine yourself – there are many more that are, without a doubt, the kind that would stay behind the curtain at the back of the video store. Ask your parents what a video store is, kids.

Recently, though, the publisher had to remove a few of its titles from the site, which it explained the reasoning behind on its account.

We ran into several issues with our all-ages games (Cho Dengekieden*Princess Evangile, and Go Go Nippon) being rated by the ESRB.

Namely, the ESRB does not allow any adult content (IE our weekly ranking and recommendations bars) to be displayed on any product pages for games rated Mature or lower. As such, we were forced to remove the catalog pages for the above all-ages versions under the threat of fines and penalties.

Speaking to import and Japanese gaming-focused site Siliconera, MangaGamer clarified, explaining that its ranking and recommendation bars update automatically as a reflection of sales. It had to decide between removing the games from its site catalog or doing some substantial updates to the code running the site. The non-AO games are still available on Steam, however.

This highlights just why Steam is so strictly opposed to adult-oriented games appearing in its store despite not having to worry about retail shelf space. Right now the only AO rated game appearing on the store is the currently unreleased Hatred. With how heavily automated and statistics-driven the Steam platform is, working adult games with graphic images into that system would likely be a logistical nightmare long before the drama of a big storefront having naughty games (as opposed to games with naughty moments, like The Witcher 2: Assassins of Kings or Mass Effect) even got started.

PC gaming is and will continue to be the only platform for these sorts of games, but even the very open world of PC gaming isn't totally excluded from the ESRB's regulations. The bigger question, I think, will be whether Valve reconsiders its decision to allow Hatred on its service between now and its end-of-second-quarter release window to keep the storefront free of AO-rated games.