Well, for those who remember PC gaming used to have a MUCH larger prescence in retail,
The issue being manyfold. For one there *are* more console gamers than PC gamers out there, like it or not. Then there are the issues with piracy and software returns, you can typically return or trade in a console game, but with a PC game this isn't generally possible. The nature of PC gaming nowadays ALSO means that used game sales aren't possible, and by selling console games they fuel their rather lucrative used game sales as well.
Then of course there is the issue that the gaming industry is pushing digital downloads, and are simply producing a lot less physical media. What's more people who buy physical copies of PC games are increasingly complaining that they have to put the games online for verification anyway, or that the disc in the box simply connects them to STEAM and gives them a code or whatever (Dawn Of War II, Mount and Blade Warband, Left 4 Dead 2, and others have all had this complaint made). Gamers not being a very assertive bunch of course go to buy their games digitally and save themselves the trouble, as opposed to not buying games at all. Pretty much giving the game industry what it's trying to force.
There are a lot of reasons for it, but yeah, PC gaming has a poor representation in retail, and really that isn't going to change unless people start demanding physical media with their wallets by simply not purchusing digital products.
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Also, one final point, the advent of MMOs massively changed the gaming landscape, especially World Of Warcraft. Generally speaking the amount of content present in your typical MMO is pretty similar to the amount of content in a single player RPG, it's just online and developed with multiplayer capability, the subscriptions involved (even considering server costs) allow for a much higher rate of profit. While there are people still developing single player games, almost everyone has gone towards the online/multiplayer thing irregardless of genere because of the possible profits. Even a failed MMO can typically out perform a successful single player game, since the company is getting that initial software sale before anything else.
Likewise, the long term investment people put into MMOs means that those people are occupied with them and not buying other games. Single player experiences largely becoming the domain of console gamers as a result. One of the big defenses made by people paying subscriptions for games like "World of Warcraft" is that $15 a month spent there is less money than they would spend to keep themselves occupied for the same time by buying other games. There is a lot of truth like that and when you multiply it by millions of people... well, you can see why PC gaming has taken a hit. Especially when you consider that you aren't even seeing that many MMOs developed because of the dominance of "World Of Warcraft". You hear people talk about how Blizzard killed PC gaming, and there is some truth to that, because of how much of the market plays WoW exclusively and doesn't buy other PC games, and how WoW dominated so totally that even other subscription-based MMOs are becoming unviable. Pretty much every MMO put up against WoW has died, or gone free to play (scrabbling with cash shops, because they aren't of comparible quality to justify a subscription fee), because all hype (and lies) aside nobody has been willing to risk developing at the same level... until now, unless EA is lying (like a lot of companies have) "Old Republic Online" is the first game to be genuinely developed with the time and money to compete with what WoW currently is (and I suspect it might succeed largely due to the fact that WoW is a *really* old game and, even with the Cataclysm update it's age shows).
