While I think that Whatsapp is to blame, Apple can't just turn a blind eye here. Let me explain.
Apple takes 30% of the price we pay for each not free app available on the App Store, right? If they make money out of this, they are also liable. Maybe they are not 50% responsible, but you can't say they are not co-responsible.
Only software which is available on the App Store can be installed on our iPhones, unless we don't temper with them. If that's the only way users can have Apps installed on their devices, Apple should guarantee a certain set the rights for us. Remember that all the Apps have to go through a validation process, so what on the earth do they look into? whether or not they look pretty?
Come on, if I'm running a business, I decide what the rules should be. And in case the business becomes a monopoly (the App Store is the only place you can get software from), the rules become even more important.
In my humble opinion, Apple should have rejected any update which efectively represents that a service, which had been provided to users before, gets discontinued unless the company goes bankrupt and closes the service down.
In other words, if the version beyond 2.8.4 cannot work on iPhone 3G, then 2.8.5 and on should have been rejected.
I know that technology is exposed to obsolescence, but there is a huge difference between not deploying new features on a specific hardware because it can't handle them well (at least that's what you can say to tease users with newer things and make they consider an upgrade), and indirectly discontinuing a product.
As an example, if I had a white MacBook and all of the sudden I could not use Pages anymore because of a 2013 update, would it make any sense? it would not! Just leave me alone using my beloved 2008 version, even if I can't take advantage of something like Documents in the Cloud.