Zach Holman does a great job of succinctly describing something that I've been having trouble quantifying into words for a while now.
Apple commands their words exceedingly well. They aren’t the originator — or even the owner — of their particular voice, but they are the most visible.
Mechanically, The Apple Voice is characterized by short, declarative sentences that are informally and personally delivered to you with a hint of smugness.
The Apple "voice", as Zach names it, is probably one of the most underrated parts of Apple's success.
Zach goes on to talk about how you can shape and choose your company or product's "voice".
The upshot: You need to do this. This matters, a lot.