Here's the #1 problem with a stylus: I'll lose it.
I hate the stylus. When I'm using it, I feel I need to "work" with it. The finger is natural and playful. Humans have been using their fingers to paint and draw long before they used brushes or pens.
A stylus is a powerful tool. To require it is folly. You have to create a platform that either ecompasses both inputs or chooses one. Simplicity would dictate the latter, and the finger is just more human.
with the psions keyboards i could get 30-40 wpm typing. with a stylus i was down to around 20wpm. typing on touch screens is a chore and stuggles approach 20wpm.
but with stylus i also had the option of doodling info on screen. at higher resolution than a finger can achieve. i could get signatures, scribble a hasty note in freehand.
i don't think it should be a requirement but rather an option. but without the option i would lose interest towards a device that has a stylus option. but even then i prefer a keyboard more and currently use a samsung galaxy pro.