Did you ever have an early Windows phone that needed a stylus because the on-screen keyboard and buttons were too tiny to operate with a finger? Or an early Android phone that would gradually accumulate background apps and grind to a halt until you fired up a task manager and manually killed them?
Jobs was right at the time - but technology moves on and mobile devices are now more powerful and being used for far more applications. You don't need a stylus to operate an iPad Pro, but having one opens up new areas of use.
That said, I'm skeptical about how successful the iPad Pro will be: I can see the applications, but wonder if they'll attract a big enough market to satisfy Apple.