There are more PC based adult games than console games. But that is due to the fact they are bought online through their independent publishers/studios, selling markets (Amazon, Ebay). Very, very rarely is a mainstream game going to be AO. In this case, Indigo Prophecy being on the list. Then again it is Director's Cut; once again, can only be bought online.
As far as AO games being sold in stores, not happening anytime soon. They are blacklisted from too many huge retailers to the point they will not make the money back with what they put into making the game. It is as if the game is in Syberia distributed from a hut, no one is going to hear about it or know anything at all regarding it.
Look at the Sexy Beach series.
GTA: San Andreas is back to M-rating. The AO rate editions (which are hard to find considering the only way to find them is online) are nothing but valuable keepsakes during an otherwise blown out of proportion witch hunt towards Rockstar. Just because it says AO it skyrockets the value of that particular edition of the game. Especially since very few are out there before they went from AO back to M-rated.
PC games are lot different from the console games in the Adult Only area. Look at Max Payne 2 game for PC; thanks to mods, technically, the game should be considered AO given if you apply the Mod you run around naked whilst playing as Mona in the game. The Sims series can go straight from T-rated to M-rated with all the Mods out there for that game! Big time! Tomb Raider 2 PC game had the nude mod (which, back then, people thought it was a code and hit every damn key in every possible way to unlock it! Hah) and was one of the first to garner the attention given Lara is the first of video game heroines here in America, especially to escalate as much popularity as she has.
Mods go back way back to the old NES days. In fact, some NES games were actually made for adults and sold out in stores! Of course, that was before the ESRB, but they were sold and they are still out there.
Thing is, official AO games are not around! They will not be made anytime soon to be sold in stores such as Best Buy, EB, GameStop. M-rating continues to push the boundaries as time goes on. Restrictions become all the more lenient. Look at an old M-rated PlayStation game then a PlayStation 2 game and a M-rated game of today! Nowadays, you get to see highly detailed and graphical glory of blood and guts! Still M-rated. AO, I honestly do not understand why that rating is still around!