Comment 9 for bug 1306078

You can receive phone calls without the Phone app running, you can continue them with the Phone app in the background, and whether you can receive them depends on your network settings. Does that mean incoming calls must be presented, or listed afterwards, outside the Phone app rather than inside? No, because those factors aren't relevant when deciding where to put calls in the overall UI. So they aren't relevant when deciding where to put calendar and contact sync in the overall UI, either.

Factors that are relevant are things like:

(A) Where will people usually be when they want to change the settings? Usually in the apps, wondering why their data is out of date. Possibly also in the data usage settings, once they exist (bug 1287267), if you've been using too much data -- but syncs are probably dwarfed bandwidth-wise by video calls and/or streaming.

(B) How complex are the sync-related settings for each account? If complex, it's a burden for each app to reimplement them, and for users to learn any variations in presentation. If simple, it's no big deal for the settings to be in each app.

(C) How often will people use a calendar or contacts app other than the default one? If very often, then it might be annoying to require people to use the default app just to change sync settings that don't happen to be represented in your preferred app. But as far as I know, there are no rival contacts or calendar apps yet.

(In the course of writing this, I realized that Phone settings probably shouldn't be in System Settings either. I've reported bug 1447601 for that.)