I was talking to a lawyer earlier today and she said something like "97% of Facebook's value is in their IP (intellectual property)" and I silently thought, no, their entire value is in the fact that they have active users. Without the network effects of active users, they are worth almost nothing.

They are like a social networking black hole, what makes them big is that they are already big, and that's all.

So if anyone starts taking away their daily active users, even if they were only taking a few percentage points off Facebook's metrics, they are effectively threatening to break Facebook's business model and put them out of business, and it makes sense to spend almost anything they can afford to neutralise that threat.