Another regular story from The Netherlands:
A 16 years old guy walks into a store and really wants a Lumia 925. He really wants it. Too bad the salesman has orders from above not to sell Windows Phone to people who find WhatsApp an important app to possess. The fellow walks out the store with a Sony Xperia Z2.
For those non-believers out there that do not believe in the importance of WhatsApp in some countries, here is your wakeup call: Nobody will buy a Windows Phone, even if he/she really wants to. Only a real techy with 'knowhow' would go against the salesman and demand a Lumia 925 no matter what.
I can promise you this:
WP sales have declined over 70% last 10 days in The Netherlands. Just an estimated guess, but not far from the truth I bet.
And as u said,the general public who are willing to give WP8 a chance will not buy a Windows Phone if there is no WhatsApp unless they are some sort of techie who really wants it. The importance of WhatsApp on a platform cannot be undermined!!