DayZ appears on Steam, just not the Standalone version
If you were ever in any doubt as to how popular DayZ is, just look at the performance of Arma2: Combined Operations. Since the release of Dean Hall's zombie survival mod, its parent game has stubbornly refused to drop from Steam's Top 10. Now, with a standalone version on the way, Bohemia Interactive seem keen to tease out every last potential Arma2 sale. To that end, the DayZ mod has been added to Steam, providing a one-click install for Combined Ops owners present and future.
It's not as flexible an alternative as DayZ Commander. That tool not only lets you patch both DayZ and Arma2 to their latest versions, but also install and update different maps and similar mods created by the community. Still, for those who like to take an extremely hands off approach to modding, a simple Steam download could be an attractive prospect.
This isn't the first time Valve have welcomed a mod onto the Steam storefront. A few years ago, a whole selection were added for games like Half-Life 2 and Red Orchestra. For some reason, the practice fell out of favour, with the Steam Workshop taking up the baton instead. Maybe this, and the Greenlight success of projects like Black Mesa, are a sign that easy and visible mod installation is on the cards again.