I spent almost a decade working for one of this country's top tier Advertising Agencies (Leo Burnett) and I can tell you exactly why Apple makes a killing on their products:
1. Brand Loyalty. Apple knows how to cultivate their customer base and sell them things they don't even know they need yet. Straight up, that's the #1 reason.
2. Additionally, Apple excels at making their devices "just work" together. Easy enough to do when you control everything from the hardware, OS, applications and utility devices from soup to nuts.
Add the "prestige" of owning an Apple device which completes the magic formula and you have a recipe for recurring sales.
It's not entirely unlike what Disney does every 7 to 10 years. Release an update to an "old classic" on the big screen and get the kids clamoring to see the movie and buy the toys that are released along with the movie.
Star Wars for example still sells MILLIONS of dollars of toys every year.
Branding, Branding, Branding. Lather, rinse, repeat!
Your number 1 reason of Brand loyalty doesn't hold water when you realize that 95% of Apple iOS buyers were non-previous owners. There is no way Brand Loyalty accounts for that. The real reason is building quality, reliable products. Do that and customers flock to your door.
In just a short eight years, iOS devices went from selling a few million in one year, to selling a grand total of almost 1.3 BILLION iOD devices worldwide. That is NOT brand loyalty. That is building products that do what they are designed to do and doing it well, in away that delighted the users so they told others.
The branding tells people to expect the best. . . and then you better make sure you follow through to provide it. That is Apple's real formula for success.