What s worth noting is that capacitive touch panels (those which respond to fingers, not the pointy tip of a hard stylus) can detect pressure. They can also do palm rejection - that is you can rest your hand on the screen and draw. At the moment, on the iPad at least, the palm is regarded as a point of contact, and the motion of the stylus is regarded as another point of contact which is moving. This is interpreted as a gesture and will be interpreted as such.

Now, as far as I am aware, in the private APIs in iOS, pressure and palm rejection ARE catered for. However, developers are not allowed to access these APIs. If you do, you tend to get kicked off the platform temporarily or permanently depending of your transgression count (the people behind Camera+ were told off for using the volume button as a shutter release before Apple started doing it themselves).

So, right now, in iOS you are getting touch pressure, but it's not being used. This is why you get these rather odd Heath-Robinson styluses which do pressure, but appear to iOS as a microphone (yes, really - they send sound to the iPad depending on pressure!).

It's mad, and IMO wrong. I find drawing with a stylus far more intuitive than with my finger.

I don't know how this applies to Android. I would expect that there are similar restrictions - either n the software or hardware.

Really?

Palm detection is a software / firmware issue so that I can understand, but how would pressure detection even work on a capacitive screen that has no pressure sensors?

The only approximation I can conceive is to interpret the contact area as pressure. That is, the harder you press the more squashed your finger and thus the larger the area triggered. It wouldn't be very accurate though, and would interpret big fingers as big pressures and dry fingers as low pressures. However, with some calibration it might provide a useful range of levels. Of course, it would either have to be built into the firmware or be achieved via very low-level system access.