I agree that using data to improve versus selling is different.
However, I do not agree that Apple doesn't have a major stake in my (and others') information. They absolutely use the data to bolster their revenue. Apple is a phone company that sells service subscriptions as an add-on; there is no way they are not using user data to position their hardware and services in a manner that generates the most revenue for them.
On the other hand, if we (hypothetically) agree that said data is used only for improving Siri, they we are forced to acknowledge that Apple is really, really, really, bad at this.