I know this will break the hearts of PC gamers, but "install base" does not equal sales, especially not in the PC industry which has a lot more free to play/demo installs and Steam bundles than consoles do. Blizzard's massive PC success also does not mean every PC developer in general is doing well. PC sales are doing better but still don't compare to the combined software sales of all consoles, and that's at a time when most consoles are nearing the end of their life cycle.
I'm not saying console games are superior, but there are a lot of factors against PC gaming. The average person doesn't want to pay for good graphics cards or build their own system. They also don't want to deal with installations and DRM. Steam has helped with the latter problem by making PC games easier to play. The former isn't as much a problem as it used to be either, these days even fairly low end systems can still work for game graphics. PC gamers still have a tendency to play a single game longer, which hurts the number of sales. A PC gamer installs a FPS and mods it when it gets old, or plays an MMO and contributes to the same game over and over through transactions. Console gamers have had a tendency to buy a game, play it to completion, then trade it in for a new game. Consoles thus make more box sales than PC games. With networked games and PC developers in the console industry however bringing games like CoD into the mix, people are trading in less and playing one console game more. Console box sales are going to decrease, and PC games will increase.