We could have waited until it hit 1 million for the sake of the bigger headline, I suppose. But I wanted to say something: the success of zombie mod Day Z couldn't have been predicted. It was a one off. A outlier. It's one of those rare and beautiful times when a game design experiment explodes into a phenomenon. No one can plan for that to happen, not really. But I can predict one thing: the companies that do not support modding will never have a zombie mod sell hundreds of thousands of extra copies of their game.
I know that for companies trying to get a game out, it seldom seems worth putting out tools for people to mod. There's the cost, for starters, and it's not always even possible - especially if you are using certain kinds of middleware or something (and I know that from first-hand experience) - and then there's the time it takes for people to get that toolset out there. Hell, it's possible that the effort that goes in might never be appreciated. Might never get picked up and used by the players.
There's a certain school of thought that looks at the lack of big total conversion mods, like there were in great waves after Half-Life 1 and Half-Life 2, and suggests that modding is "dead." As usual with claims about the demise of a form, those claims start to look exaggerated when you look at what's really going on. It's something that we're going to talk about in detail in the near future, but it's arguable that mods are more interesting now than they have ever been. Just a quick glimpse at the Steam Workshop for Skyrim suggests that even though those grand overhauls are distant, the modding scene is far from idle.
For BIS, of course, the policy of supporting player-generated content and modification would have been a fundamental attraction even with Day Z. For that game the staples of other games - things like a single-player campaign - are almost incidental the toolset they provide. It's something of a vindication that those tools have not only sold copies of the original game, years after release, but now look set to generate a new, standalone game.
Everyone else making games needs to look at that, and to consider that providing tools might be mean more than simply letting your community provide for itself, as Bethesda has done with The Elder Scrolls games, it might be the equivalent of buying a ticket in a very lucrative lottery. We might not get a new Counter-Strike every year, but that lottery is definitely still running.