Minecraft the game does not generate a continuous income after the initial sales, but recently they started an official multiplayer server hosting service (called "Minecraft realms"). You can buy a private server for $10 per month.

Given that Minecraft is played by a lot of kids whose parents whose parents or themselves do not know how to set up a server, I think this is a very viable monetization strategy, albeit launched a bit late.

Of course, there have been 3rd party commercial hosting services for Minecraft for a long time, but again, it's not something kids and their parents go after.

Hell, I know how to set up a server but I am considering hiring a Minecraft realm for the winter months, just because it is less hassle than setting up a server and the price is reasonable.