As Apple claims, there is end-to-end encryption. The weakness is in the key infrastructure as it is controlled by Apple: they can change a key anytime they want, thus read the content of our iMessages.
Also remember that the content of the message is one thing, but the metadata are also sensitive. And there, you rely on Apple to carry your messages, thus they have your metadata.
Számomra az érdekes ebben inkább az volt, hogy mennyire bonyolult rendszer az iMessage, nem is gondoltam volna.