Found this thread while looking for the answer to the same question.
Disappointed that no-one really answered the question I played around with the trackpad and realised that it is almost impossible to move the pointer with the palm while writing, no matter how lightly I touch the trackpad. Selecting/deselecting "Tap to click" doesn't change anything. When trying the same thing with a 2 year old MacBook Pro I had no problem making the mouse fly around on the screen with the palm.
So it seems to me that the "Ignore accidental trackpad input" and "Ignore trackpad when mouse present" settings are no longer necessary with the Air 2.