That is a LOT of money. That being said, I use WhatsApp every day to chat with my friends around the world and it's really excellent. I know it's used a lot in other parts of the world even more, so I doubt this purchase is focused on US markets. It seems that every one of my Arab friends uses WhatsApp to talk to their families back home (and they use it at home, too). I don't know about other regions.
WhassApp is the standard in Mexico. It replaced Windows Live (MSN) Messenger after they killed it by trying to make everybody switching to Skype and the interest of the people shifted to mobile.
And also, think - MSN had everyone's friends info, as well as frequency of contact and so on. It would have been a perfect way to launch a real social network. MSN fumbled that too.
A comedy of errors.