You're probably right. In that case, I wonder if Wacom could make some kind of a "frame" around the iPad that can triangulate a stylus and receive pressure data, etc?
The Wacom Intuos Creative Stylus (what a mouthful) uses Bluetooth for pressure, which is similar to the Pogo Connect and Adonit Jot Touch styli. What the OP want is perhaps something similar to the iPen 2 <http://www.cregle.com/>, a pen and receiver combo that captures pressure sensitive data.