Nearly a month ago, we first reported that gaming giant EA was looking to buy Playfish. Today, the deal is official. The purchase price is $275 million in cash, with $25 million in “equity retention arrangements,” according to the press release, as well as “a maximum of $100 million” based on meeting performance milestones over the next two years.

The significance is that EA, one of the largest video-game makers in the world, believes that its future is tied up with social gaming. Playfish has distinguished itself by creating well-polished social games and gaining tens of millions of users.

In fact, as Inside Social Games readers know, we broke the story around a month ago. From our first article:

We have a few more details on what has supposedly been happening with Playfish. A reliable industry source says EA may have even acquired the company several weeks ago, with an announcement possibly happening in the next few weeks. We believe that Playfish could be on track to make as much as $75 million this year.

We and others had heard the deal was for $250 million at the time, but we heard a couple weeks later that it might be more. From our second article:

EA has been doing due diligence on Playfish, we have heard from multiple sources, meaning it has been going through the company’s financial reports and other information to determine that it indeed does want to make the purchase. We do not know if the deal has fully closed yet. Our understanding is that Playfish has been in a “no shop” period, meaning it won’t talk other potential acquirers as EA completes its review. However, some sources have previously said that the deal may have already closed. We have also heard that Playfish’s banker is J.P. Morgan….

One reliable industry insider we spoke with believes the amount is “north of $400 million.” But we have also heard that the number was “less than $200 million.” Hmm. Perhaps the “north of $400 million” number includes some sort of earn-out plan? For sake of comparison, kids virtual world Club Penguin sold to Disney in 2007 for $350 million, with the possibility of earning another $350 million based on performance over the next years.

It’s not clear when the deal closed. EA is announcing its earnings today, and it is has been in its quarterly quiet period until now — which explains the company’s silence on the rumors over the last month.

Most of Playfish’s games are on Facebook, and the largest one is virtual pet-caring game Pet Society, which has 21.5 million monthly active users and 5.24 million daily active users. The second largest is virtual restaurant game Restaurant City, with 18.1 million MAUs and 5.30 million DAUs.

Like most social gaming companies, EA makes the vast majority of its money through direct payments. While it does run some advertising offers, the offers are from TrialPay, a company that focuses on running high-quality ads from major brands. Many offer companies have been running low-quality offers like mobile ringtone subscriptions, and they’ve have been coming under heavy criticism for it. But Playfish’s reliance on direct payments and high-quality offers means it has not and will not be much affected by these issues. Indeed, the biggest way it is affected from that issue is that many people outside the industry have come under the mistaken impression that social games make most if not all of their money from offers.

The bigger issue, now, is that Facebook is introducing a wide range of changes to its developer platform, getting rid of notifications and other features that apps currently use to reach users. Playfish is likely to be less affected than some other game developers, as it has focused on making its games fun, first; instead of users getting tricked into sharing the game with their friends, they happily do it. Now, with EA’s money and large pool of gaming talent, Playfish will be especially well-positioned to compete against market leader Zynga. For example, Zynga may spend up to $50 million this year on Facebook ads, to help it gain more users. With EA, Playfish can easily do the same.

This is also a nice exit for a couple venture firms: The company has raised $21 million from Accel Partners, Index Ventures and Stanhope Capital.