I think the parent put regional in double quotes for a reason, he/she just meant to say that it was more popular in certain part of the world than other and it's 100% right: It used to have 100 million users and was #1 in 11 countries[1]. Back in 2003 this is quite impressive!
Bashing on 'iOS users from the bay area' makes no sense, the parent also implies in his post that he is from Europe.
And as a non-iOS user, not from the bay area, I have rarely see people using WhatsApp, neither in Europe, nor in the US. The only few people I've seen using it is foreigners who want to stay in contact with relatives/friends in an country where WhatsApp is popular.
[1]http://news.microsoft.com/2003/05/12/100-million-customers-a...