A: (Scott Forstall) You don't have to. The user just uses things and doesn't ever have to worry about it.
A: (Steve Jobs) It's like we said on the iPad, if you see a stylus, they blew it. In multitasking, if you see a task manager... they blew it. Users shouldn't ever have to think about it.
The point was that using a stylus as intermediary when doing basic interaction with a touchscreen is indirect/awkward and unnatural (the mouse is too, frankly), not that nobody should ever use a stylus for drawing.
Styluses clearly have a big precision (and visibility) advantage vs. tracking a whole fingertip touching/sliding around the screen (i.e. if we compare inherent human capabilities, not specific hardware), but relying on a stylus is also much more prescriptive about acceptable hand movements, and all of the stylus-first mobile devices pretty much suck compared to finger-based multitouch, in practice.
And now that Apple's on board with USB-C, which can do video/power/peripherals, it's not inconceivable that a Monitor+USB hub would be all you need for a plug and play iOS productivity station.
It would be a trivial firmware change for the next release of iMacs to support, and an extension of their existing target-display mode.