FORTUNE -- Facebook (fb) set the tech world buzzing this evening, by announcing plans to acquire virtual headset maker Oculus VR for $2 billion. This marks the third time Facebook has strayed from its M&A strategy of acqui-hires. Unlike the first deviation, however, the most recent two targets have generated some real revenue.
Typically, Facebook buys a small startup and folds its product into its own, shutting down the startup. It's mostly a talent play, and sometimes a technology play. Facebook has followed this strategy 42 times, with three exceptions.
Three very big exceptions.
The first was Instagram. On the eve of its IPO, Facebook paid $1 billion for the fast-growing app. In a "fairness hearing" on the deal, when Instagram founder Kevin Systrom was asked how the company makes money, he cheekily answered, "That's a great question. As of right now, we do not." Zuckerberg promised Instagram it could operate independently of Facebook.
2. Mobile messaging
Similar story for Facebook's most recent whale of an acquisition, WhatsApp. Facebook paid $19 billion for the app, which,
like Instagram, makes zero dollars in revenue charges $1 per user per year. Update: WhatsApp is estimated to have around $20 million in annual revenue. Its founders famously opposed advertising, and Zuckerberg promised them it would keep WhatsApp ad-free. He also promised WhatsApp it would remain independent.
3. Virtual reality
And now Oculus VR. Today's deal marks the third $1 billion (or more) Facebook acquisition, after which the acquired company will be allowed to operate as an independent entity.
Like WhatsApp, Oculus VR is not a zero-revenue company. Oculus made money by selling pre-orders for its developer kits, which cost $350. The first version (Oculus Dk1) cost $300. That means Oculus had brought in around $23 million in revenue.
That's nothing compared to how much venture funding Oculus raised ($93.4 million). Or how much Oculus' early investors made on the deal. (In June 2013, Spark Capital and Matrix Partners invested $16 million at a $30 million pre-money valuation. They both reinvested when the company raised $75 million more from Andreessen Horowitz.)
On a conference call today, analysts probed Zuckerberg for hints as to how Facebook will monetize the acquisition. Zuckerberg hinted at virtual goods in virtual reality-land, or possible ads. But he stressed that the first few years of Facebook owning Oculus will be about investment and development. "For the foreseeable future, the mission is building out the product using the levers that Facebook has to make the product affordable to people and make it ubiquitous."