Don't look for logic in these sorts of aquisitions anymore - its another tech bubble getting ready to burst.
Nothing is bursting. Capital suction has little or no effect in the digital world these days. No one cares if you burn a million or a billion. It's about data and market share, revenue be damned. Do you think running whatsapp indefinitely cost any more than a crew or two of developers and some rackspace in some datacenter nowadays? Twitter is run by 13 people. 13 people!
They don't care about revenue, they want your data and they want lock-in. And they'll trade lock-in for data and omnipresence at any time.
It's about 4,5 billion people on this planet about to be connected to the internet in the next few years, with devices that cost less than what a fourtnights worth of Starbucks costs us.
We are moving head on into a post-scarcity economy, at least in terms of digital connectivity - from there on out it's all about attention and mindshare. The purchase might bomb, yes, but it might as well just turn out to be a real bargain. And if it bombs it won't even do a blip on FBs bank account. And others won't care either. Those who have VC can buy into WhatsApp like startups for peanuts because deving, deploying and scaling has become so dirt cheap. So even if they all bomb we'll be back to business as usuall 4 weeks into that.
The world is changing, and it's changing fast. The dot-bomb era was just people getting ahead of them selves in a way that wasn't good for them. The hardware wasn't there, Databases and IDEs costed more than luxury cars, and what passes as a toy today was a cray workstation in 2001 that would set you back 30 grand. It was silly back then. It isn't now.
Reality is catching up. Fast.
I wouldn't hold my breath for any bubble of sorts bursting any time soon.
My 2 cents.