This was actually a very useful change to me as an IT person. Because the OS and its updates are not tied to a specific AppleID, a user is able to install OS updates without logging in to the app store, which if memory serves was not the case a few years ago. This was a constant source of annoyance when managing a small workforce of Macs, whereas now I don't need to create a "dummy" AppleID for each user to enable OS updates if they aren't logged in themselves. ...The reason is that prior to Sierra, purchases (downloads) were tied to your AppleID, so they had to have been previously "purchased". Since Sierra, installers are no longer tied to your AppleID, so they aren't considered as purchased software any more.