Guran,
I think that inertia is involved.
Agreed that when you close the airflow the concertina end will cease to move, but this is not instantaneous. It will form a partial vaccuum and then oscillate until the frictional forces in the bellows bring it to rest. Now, I think that that is going to take longer than the time taken for me to start playing another note in the opposite direction.
Also it does not allow for me playing a drone (as I quite often do for short passages of a tune as well as whole tunes) which negates the "airflow being closed" effect.

I don't think that I would want to go to too large buttons, I like to be able to detect the edges with my finger tips. It is just the increased pressure in the centre if they are too domed that is the problem.