If that's the case, how long after the purchase of a new iPhone does your imessage subscription expire?
Of course it does not. The per user cost of delivering imessage is so low, Apple doesn't care about the individual user. In bulk, enough people are buying new iPhones to cover the ongoing cost (and then some).
Well WhatsApp and Telegram are free, so it's hard to make that argument there, but my understanding was that the problematic behaviour was for Apple to make the performance of those devices otherwise worse without disclosing the reasons why, which caused people to upgrade earlier than they otherwise would have.
The analogy would be for WhatsApp to make it take artificially longer to send messages on Android 4.4, which I think people would have a problem with but they have no good reason to that.
I can't speak for Telegram, but in the case of WhatsApp, they decide to deprecate particular SDK versions when the usage of those SDK versions drops below a threshold, and it's against their interests to do otherwise, because they lose market share and they are making a tradeoff between engineering support costs and users.
Of course it does not. The per user cost of delivering imessage is so low, Apple doesn't care about the individual user. In bulk, enough people are buying new iPhones to cover the ongoing cost (and then some).