If they want to support Siri on phones other than the 4S, the way for them to do that is to put the real, built-in Siri on other phones. The Siri app is outdated and essentially nothing like an Apple product at all.
Your analogies don't work because a.) The Siri app was free and therefore no one really owes anything to people who used it and b.) No one before iPhone 4S buyers was ever promised any sort of feature like Siri. In fact I'm guessing that 95% of iPhone 4 and earlier owners have no idea that anything like Siri was even available.
So Text Messaging is a free app and no one would owe anything to to people who used it if Apple eliminated it based on your argument? And further, what your saying is any free app out there, can be eliminated at any time, and no one should care, because nothing is really owed, is that correct? Have you ever watched an Apple commercial? Almost everything they advertise is 'There's an App for that' and almost all of the advertised apps are 'free' apps. Do you think its just possible, that a few people may have just bought an iPhone because one of the selling points are free apps? Free apps, like Siri perhaps?
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They've done that before. iTools -> .mac. iTools was a free service, then they switched gears and started charging. Only now in light of the competition they have decided to switch gears again and make iCloud free.
As for the notification, I think you're having a difficult time convincing people that they did not notify users. Could they have done that a better way, perhaps but apple is not a company known for its communication skills.
Regardless of all that, this is a moot point. The bottom line is, if you want Siri buy an iPhone 4S, nothing else will change that.
For apple, as others stated, they made a business decision to only have that on the 4S.
Actually, I'm not trying to convince anyway that they didn't notify users. I've consistently pushed forward the point that they didn't properly notify users, which is different. Even today, the cryptic 'unable to connect to server message' is all the notification existing users get. And I disagree, Apple does usually communicate well - in fact, it has such a loyal following because its learned to communicate tech to just about any consumer in a great way. They just failed on this decision relating to shutting down Siri.
As far as the business decision, no one is so naive not to believe this wasn't a business decision. If enough users have a problem with the decision though, they could always change it. I'm sure Siri is undergoing programming changes since its release to 4S users and maybe they will find a way to make it work again on the iphone 4 without too much more overhead/support in the future. But without consumer feedback such as through this forum, there probably would be no point to even trying. I also wonder, now that Siri has been released to many iPhone 4S users, what if the business decision is to discontinue it when the iPhone 5 is eventually released.
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Don't buy the phone - as consumers our power comes with our wallets. Don't like how apple doing things, then buy another phone.
That's a pretty broad conclusion. Since I've owned every iPhone model to date (except the 4S so far), I would say that I probably like the phone. Wouldn't you? Doesn't mean I like everything Apple is doing (or ever has or ever will). I personally think Apple is facing a crossroads in the near future and the more consumer feedback they listen to, the better positioned they will be. Consumers have wallets as power, I agree, but they also have voices. If they didn't, MacRumours wouldn't need to exist.