Re: I've been trying it. (@JDX)
The boring historical version is that PostScript was the standard for high end printers so several vendors built desktop platforms around PostScript as the description language for drawing on-screen rather than rolling their own versions of QuickDraw or GDI or whatever — Sun was one (with NeWS), Next Computer was another. PostScript is a full programming language* and when adapting NextStep into OS X Apple looked at the licensing fees for the implementation NextStep had used and decided instead to keep the same primitive drawing semantics but do away with the language.
Separately, over at Adobe they designed PDF as a record of the output of a PostScript program (so, to spend storage in order to save on complexity, at least initially). So PDF also inherits the same primitive drawing semantics as PostScript.
That made it easy for Apple to add PDF rendering and print to PDF to its operating system and all applications just work. There's no translation layer whatsoever, the drawing operations are just serialised and stored or deserialised and performed. As iOS is a close relative of OS X, with exactly the same graphics operations and frameworks, the same stuff just naturally carried over.
The same is not true of Windows because even once they were looking to do something beyond the GDI Microsoft insisted on inventing its own document format in XPS and tied WPF, its modern drawing framework, around that.
(*) trivia: the original LaserWriter — a key component in the early desktop publishing revolution — had a CPU 50% faster than the Mac it was meant to be attached to because it had to do all that high resolution rasterising.