I could be mistaken but I'm sure I saw somewhere before that in the first part of the flight, during Abort Mode 1-Alpha there was a delay of 2 seconds between the abort sequence being triggered before the LES pulled the CM off the rocket. In the event of the S-1C blowing up there may not have been enough time to save the astronauts.
Had Apollo 11 failed because of a Saturn V explosion then there could well have been a lengthy delay before 12 was launched until NASA was sure it had fixed the problem. Another possible factor is that if the Saturn had exploded close to the ground then it's explosive force is just under a kiloton of TNT so LC-39A is going to be a smoking crater and although it's miles from the explosion LC-39B and some of the ancillary structures are going to be damaged. So even if they got the rocket fixed quickly they may not have had anywhere to launch from. I think one of the N-1's failed in this way and it completely destroyed it's launch pad.