dynamic control: sudden ff to pp

[demented cow]

Suddenly going from very loud to very soft in the space of one note/chord (=call this the sudden-pianissimo or sp effect) isn’t heard often, though I can imagine it being beautiful or even heart-stopping in many pieces (whether or not the composer demands it). Some questions on this:
A.   Does anybody know how easily professional/famous pianists can do sp effects in very fast passages. Say a composer asked a pianist to play a very fast four-octave scale with the 1st ocatve ff, the 2nd pp, the 3rd ff and the 4th pp. Would the average professional have to practise for long to be able to do this well? Or is this a standard skill or is it unattainable by (most) humans?
B.   I (an amateur) am lousy at sp effects: I tense up, I have to pause before playing the soft notes (which may fail to sound anyway). Has anybody successfully worked on this sort of problem? Or is the problem (as I suspect) one which I can’t work on in isolation, a sign that my whole technique is all ph*cked up and needs a complete overhaul?
C.   "Playing pianissimo is the basis of piano playing. You should have to do something extra to play louder than pp. You should not have to do something extra if you are getting softer." Discuss.
D.   Can anybody recommend recordings which have sp effects in them that they like? (The sudden drop in the slow bit of Horowitz’ Funerailles is the best I can think of, but I'm having trouble thinking of a similar drop in a fast passage.)
Thanks,
The Cow