For me the biggest feature is being able to type questions in private, like Fantastical. I use Siri when I'm alone at home or in the car but I regularly find myself checking before using it. It's awkward saying "remind me to pick up extra maxi-pads for the wife on the way home" to siri when I'm at work within earshot of my co-workers. Even less private things than that can be weird.
The palm vx, did not have a capacitive touch screen with an interface designed for touch. Adding pen support to the iPad does not affect the interface. I'm not sure how your comment is relevant to the conversation?