Thanks for reading and for your comment. I completely agree, the valuations on these companies has gotten out of control and there's certainly a large amount of luck involved with being in the right place at the right time. At the end of the day, it's just about how much potential revenue Facebook sees in these new 450M members and what that's worth to them.
PS- PolicyMic ran a great article called "15 Things Cheaper than WhatsApp", including the entire world's music industry and the cost of providing clean water to the entire world for a whole year. I'd recommend checking it out: http://www.policymic.com/articles/82945/15-things-that-are-cheaper-than-whatsapp