The key differentiating factor is that the iCloud heralds an era wherein all of your data is decentralized, all of the time, and that this is the default for all users, on all Apple devices, all of the time.
You are correct, for all definitions of "decentralized" that are "rigidly centralized, almost appearing decentralized because centralization is so far outside your control"
That's why I like the Apple vision - it leaves my data with me. It doesn't lock it up in a cloud somewhere.