I believe there was an effort to simulate pressure sensitivity by measuring the change in surface area of touch points. When you tap lightly you only touch a small area, but the harder you press with a soft stylus or fingertip will increase the surface area of touch point, which could be interpreted as more pressure by the app.
I agree that it should come to the device whether hardware or software. However I just want it for pen input.
Also, there is already an implementation which utilizes the accelerometer to sense a harder press vs softer press. Example is piano in GarageBand.