OOps! Sorry Captain Stable, did not intend to upset/offend yourself or any other folk..(not my style). Sincere apologies if I have. As you said you didn't have your books to hand and I am guessing that:
a) 50% 'ish of pilots would have agreed with you.
b) It is not the sort of "rivetting fact" that one retains uppermost in one's mind midst all the other "stuff" you guys/gals have to draw upon in your everyday line of work.
c) reason for conditions are based on a percentage probability of an accident/incident making both r/w's inoperable at the same time, when required in extremis, is so remote as to be considered an "acceptable risk".
Pax Manifest!!