They can't change the terms on a product they have already sold to you, but new versions of the OS and dev tools are new products with new features. If you want the new features, you can choose to accept the terms, but you don't have to.
On the user side, there are security updates. Yes, you can refuse to install OS updates that patch vulnerabilities, but obviously that's a big problem for the user. And eventually the vendor stops providing security updates altogether for the hardware.
On the developer side, you can't really refuse to use the new versions, because they are required to support your software for the latest OS versions, which is where your customers will be. So if you don't, you lose your customers and go out of business, which is not much of a choice.
It's untrue that updates consist of nothing but new features.
