If you can call a P/E of 800+ "very profitable"? Making $20M a year profit is no small thing at all, and I'm sure if it was bought for a billion, you'd see far less comments on the subject.
Goes to show that only 20 Million out of 430M paid the $1/year (which has something to do with it not being charged everywhere and people having a 1 year grace period and a majority of their target market having no credit card (young audience in emerging markets)).
Let's see how Zuckerberg plans to change that drastically.
32 employees * 100,000 = 3.2 million
Let's say a million a year for office space and another million for infrastructure and bandwidth, seems like they were fairly profitable for what they had. No idea how Facebook plans to recoup $20 billion though.
Twitter generates about $2M in revenue a day. And they make nothing since they're not profitable. So compared to Twitter, WhatsApp is undefined profitable.