The distinction (I believe the original quote is Picasso, and the difference is that the great steal while others borrow) is that once you've STOLEN an idea your version is so much better than what you took the whole thing becomes YOURS. Borrowing an idea means that your version ends up simply looking like a lame attempt to copy the older idea, and people prefer the older idea.

So while there were GUIs before the Mac, once Apple had stolen their ideas and transformed them the stuff that had come before simply looked like crap. Similarly previous attempts, including by Apple, to create tablet devices look like crap beside the iPad.