I assumed someone would say “but this is interface design, not literature”. My point, if you read it, is that to write this analysis without so much as a reference to good grammar is just a bit weird. Surely that should be the start point.
Any phrase in a book may be used by the author as a chapter head or subheading. It may comprise a grammatical sentence, a fragment, or a single word. But, conventionally, it would be written in title case.
Yes, of course. In that case it is used intentionally as a chapter head or subhead. It becomes a title. But this, for example:
Turn On Location Services to Allow “Weather” to Determine Your Location
…isn’t. It’s an instruction and a fully formed sentence that should be written as a sentence.
I doubt the person who carefully considered Apple’s style guide ever intended for that kind of interpretation of their rule. My guess: it was an accident; slavish misapplication of a guideline that was intended for titles. But even if it was intentional it’s still weird, uncomfortable to read and widely perceived as wrong in its particular context when judged against the norms of grammar and style. Which, I would say, is the underemphasized point.