AO-rated games are few and far-between simply because none of the big three players (Microsoft, Nintendo or Sony) will OK their release on their systems. That leaves the PC as the last bastion of the Adults-Only games, but there's one other major factor that prevents the PC from being overrun with these titles: Wal-Mart.
Wal-Mart refuses to carry software that is not rated by an official ratings association (a stance they have held since 1995), as well as any software title on any platform rated higher than an M/17+ just as they refuse to carry any movie with a rating stronger than an R/18+, which is why you won't find anything that carries an NC-17 or X-rating on their racks. And given that Wal-Mart is one of the largest distributors of computer and gaming software in the world, making a game with the AO rating is essentially a kiss of death because 95% of the gaming world won't even be able to find the title on store shelves. It doesn't prevent you from releasing it for purchase on the web (though any of the big 3 will sue you if you create a game for use on one of their platforms that was not given their seal of approval), but your sales will be nowhere near what is necessary to cover the cost of development, and you can kiss virtually all of your potential sales to casual gamers goodbye.
So, when Wal-Mart, Sony, Nintendo and Microsoft all stand between you and your target market, it's game over. And you're all outta continues.
*huggles*
Areala