"The 747 was designed when we had little to no history on jet engines in commercial service. Hence the designers designed them to the mathmatical probability of 10 to the -9th criteria and came up with 4 engines as having little to no chance of losing all 4 in the same trip. Now we have tons of data on engine reliability and have much improved reliability. Hence the 2 engine long range aircraft emerge."
Sorry, 747FOCAL, and far be it for me to challenge you on a subject so squarely in your back yard, but this statement just doesn't remotely correspond to my recollection of the B747 design evolution process.
Firstly, I think the guys who worked on JT4s or JT3s or Avons or Conways for years before the CX then B747 programme would take issue with the "little or no history" bit, not to mention the enormous significance of B47/B52 experience. Secondly, when Boeing wanted to build people a great big plane in the mid 60's to carry twice the B707 payload it HAD to be four engines, because Pratt's could barely exceed 40,000 lbs of thrust with the first JT9D. Don't you remember what an incredible achievement that thrust level was at the time? The payload/range goals and attainable thrust levels were the first-order determinants of the number of engines, not the reliability.