This makes the iPad ("finally") a legitimate successor to the Apple Newton MessagePad 2100 (from the 1990s), and incidentally the first iPad that I personally am excited about buying.
The stylus is not just some accessory. Real stylus support is a fundamental advance that revolutionizes the device. This is every bit as significant (for the iPad) as a keyboard-only computer finally supporting mouse input.
(To stretch that analogy a bit, the stylus products available for the iPad so far would be like wiring an Atari 2600 controller to the PC and being able to do rudimentary cursor movements with it.)
The stylus was a fundamental advance for humankind, too. The first stylus was invented about 30 seconds after the first caveperson discovered that flat surfaces are good for drawing on with your fingers. And humans have used them ever since.
Steve Jobs was right that "If you see a stylus [as a requirement for basic input and manipulation of the device], they blew it [if they meant their device to be a mainstream consumer product]."
There's a corollary, though: If a tablet meant to be directly manipulated doesn't support a stylus, it is going to be worse than a simple piece of paper and a pen for a wide variety of everyday tasks. (Meeting notes, class notes, sketches, etc.)
The iPad has sucked at all of those things, forever. (Despite the amazing (truly!) software enhancements that have made fingerpainting pretty expressive.)
I cannot think of a more fundamental advance Apple could have bestowed upon the iPad.
They are indeed playing catchup -- I have all the iPad generations at work and have never used them for much. I do use the Microsoft Surface Pro 3; it has a lot of shortcomings but is hugely, objectively superior to any iPad for taking notes (in just about any setting one would take free-form notes in). But it's heavy, fans, Windows, etc.
I am a refugee from the end of the Newton days. In college, I took all my notes on an MP2000 and it was amazing. It totally worked, for text and diagrams, on balance better than paper. And nothing since then has been both highly portable and as good at note taking. The iPad is better than the Newton at lots of things -- movies and media consumption come to mind () -- but even almost two decades later, no iPad has never been even close to as good as the MP2100 is at taking notes.
So, $1050 for the new iPad Pro plus the stylus? Funny coincidence, that's exactly what I paid for my last Newton. Sign me the fuck up; I'll take a couple.