Well, OS X already has a form of offline voice-control, so obviously an internet connection is not absolutely mandatory for these things.
It's a bit buried though; you have to go to System Preferences -> Dictation & Speech and turn on Use Enhanced Dictation, then go to System Preferences -> Accessibility -> Dictation and Enable the dictation keyword phrase.
By default it's "Computer" but it can be "Hey Siri" or anything you want, so you can say things like "Computer, switch to Safari" and "scroll to the bottom" etc.
I wonder why Apple hasn't advertised this more prominently. It seems to be an edge over whatever's available in Windows.
It's a bit buried though; you have to go to System Preferences -> Dictation & Speech and turn on Use Enhanced Dictation, then go to System Preferences -> Accessibility -> Dictation and Enable the dictation keyword phrase.
By default it's "Computer" but it can be "Hey Siri" or anything you want, so you can say things like "Computer, switch to Safari" and "scroll to the bottom" etc.
I wonder why Apple hasn't advertised this more prominently. It seems to be an edge over whatever's available in Windows.