Games tend to have a very short life on store shelves; if you don't make your money back in the first few weeks, you'll likely not have another chance. But instead of accepting the status quo, Valve asked itself what happens if you continually update games and keep the online community engaged? It turns out that gamers keep buying, and buyers keep playing.

We caught up with Doug Lombardi, Valve's vice president of marketing, to talk about what you get from continually evolving your games. "Ongoing development for our products has been a staple for Valve since Half-Life 1," he told Ars. "Whether it was shipping new maps for HLDM, full add-ons for free like Team Fortress Classic, or the Software Development Kit, which led to amazing mods such as Counter-Strike, Day of Defeat, etc..., it has been a common practice here that is considered throughout the development of each product."

There is also no set strategy for what comes after launch. "The roadmap for every post-launch release, however, varies with each product. Development for Team Fortress Classic, for example, happened before HL1 shipped, and it was originally planned to be a paid add-on. Then, just before launch, the decision was made to add it to the first Game of the Year Edition, Half-Life: GoTY, and release it online, for free to existing owners of HL1."

The trick is to give the team the freedom to explore the game and find out what it needs, and you can't do that with any kind of map or strong pre-release plans. "In similar fashion, new content for TF2 was planned before it shipped, but certainly every new item and achievement that has been made available during the course of the past 18 months was not set in stone years ago," Lombardi explained. "Keeping things a bit open allows Valve's designers freedom to consider what's working in the community and incorporate feedback into future releases."

The question is, how do you know when to stop evolving a product and start throwing your efforts into the sequel? Most companies hoard ideas and updates, and when I bring up the question of whether new ideas should be released as an update or held for the sequel, Lombardi seems slightly impatient at the notion. "Good idea. I just spoke to Robin and we're going to hold the next update for TF3."

"Seriously, that's not how Valve approaches it at all. We have no idea what TF3 is. But with each update, we're getting a better handle on TF2."

This isn't all rainbows and unicorns mixed with a heaping helping of fan service. Left 4 Dead is game that has been handled with almost surgical precision to keep sales steady. The game was released to positive reviews and strong sales, and now the free Survival Pack has been released to get gamers back into the title, and to draw in a new audience who may not have thought the game was worth the asking price in the past. Of course, if that wasn't good enough, Valve allowed players to try the game for a full 24 hours this Friday and the offer was extended. To sweeten the deal even further, if the gamers who participated in the trial decided to buy, Valve added a sale that cut 40 percent off the cost of the game. It's a hellishly effective strategy to get your money.

All this happening together is no coincidence. "The updates cause an incredible spike in sales. And when the update is offered in concert with new Achievements, new media, such as a new 'Meet the...' movie, and a promotion, such as a Free Weekend and/or limited-time price drop, the spike is even higher," Lombardi told us. "With every release, we witness a spike in sales on Steam and at retail."

The strategy works. Left 4 Dead and Team Fortress 2 are still discussed on the gaming blogs, and they enjoy a strong online following that waits breathlessly for the next update. When the sales start to dip again, Lord knows there will be another sale or content pack to keep interest up... not to mention sales.