Earlier quoted context omitted.
Yes, but... With a sufficiently widespread third party library they risk a backlash with their userbase. Social networks depend so much on the network effect to bring in users that cutting out a large chunk of users all at once because the protocol changed could cause more users to drop out. Thinking about it, I wonder how much AIM and MSN Messenger's fights against third party clients messed up their user bases.
Their userbase uses the Whatsapp app that comes bundled with their phones on many intl carriers. I don't think they care about the 0.0001% of their userbase that uses third party clients.
I know that you can't used the outdated version on Android for much longer without being cut off access.