I think this refers for your phone and computer to integrate. For example:
- When your phone is near your computer, your phone ringing will pop up a notification on your computer, which allows you to answer it via OSX (e.g. using headphones plugged into your computer).
- When your phone is near your computer, Messages.app can text message via your iPhone.
From here[1]:
> When your Mac computers and iOS devices are within Bluetooth range of each other (about 33 feet or 10 meters), they can automatically “hand off” what you’re doing from one device to another. For example, you can start writing an email in Mail on your iPhone, then instantly pick up where you left off in Mail on your Mac.
> Handoff works with several apps that come with OS X Yosemite and iOS 8: Calendar, Contacts, Mail, Maps, Messages, Notes, Phone (iOS only), Reminders, and Safari. It also works with Keynote v6.5, Numbers v3.5, and Pages v5.5 for Mac, and Keynote, Numbers, and Pages v2.5 for iOS. Third-party apps may also work with Handoff.
You can also make calls or send texts from a mac if your iphone is nearby.
I've customized mine with touchegg (made for GNU/Linux systems) and it does everything I've seen Mac users do and more. Need no Apple for that one, and there are probably Windows tools as well though I wouldn't know which.
> 6: Handoff in OS X with my iPhone is such a great convenience.
I don't know what "handoff" is, but regarding interoperability, a rooted Android phone running GNU tools (e.g. Linux Deploy app) is a dream when you have a GNU-based laptop/desktop operating system as well. I can browse my phone like a network drive and getting a shell is as easy as connecting to any old linux server.
This doesn't make your other points less valid, by the way. There is surely a good argument to be made for OS X.