Gaming isn't making all those Billions off of PC users, it's dedicated game consoles that make all the money. The reason console gaming is growing so much compared to PC gaming is because of ease of use, which is the main reason web apps are so popular.

PC gaming is broken precisely because of the problems with writing software for the millions of PCs out there. Web development, on the other hand, is like building a game for a console, you don't have to worry about all the hardware that's out there, you just write to the environment. While writing web apps is not like having a unified development environment it's a lot closer than trying to write a program that will run on every hardware configuration out in PC land, and Mac, and Linux, and Solaris, etc.

Just as console gaming is slowly killing the PC gaming industry web applications will slowly kill classic PC applications. That doesn't mean that the PC is going away, but the future definitely lives on the web.