Further, who do you think customer's call for support?
Now you know why carriers are hesitant about frequently updating a product they've already made a sale on. If an update breaks something, guess who pays the price?
Not defending them, and it's not the only reason, but it's a big one.
Whether or not they should have a say is a great question. Now that they do, I'm not sure it can be taken away without them simply choosing the next os that they do have more say over.