"If anything, as engineering friends have explained to me, frames work harden and in theory that would make them stiffer and at the same time closer to a failure."
Steel fatigues. This is a sad fact of life. That said, a wet-behind-the-ears mechanical or manufacturing engineer can easily design a steel bicycle which will be able to withstand all the deformation cycles predicted for 100+ years without showing any signs of fatigue problems.
Maybe all those Eddy frames Chuck saw in the field in back of the factory were built to be so light that they would only survive one race with Eddy hisself doing the flexing/fatiguing. I tend to doubt it, but it's possible.
I also remember tales of a super thin-wall Prestige Nishiki rolling into Moots underneath a guy who came to be known as "Big Smitty." He was 6'7", ~350lb. He was touring from California to the East Coast. By the time he got to Steamboat Springs, the bike has practically dissolved underneath him. Metal fatigue was a big factor in this. We built him another steel bike with an extra tube between the downtube and the top tube. Made it out of tandem tubing. Now THAT bike never fatigued. In fact, it made it through being run over by his van a few years later, although we did have to do some frame repairs at that point.
Yours,
Forbes Bagatelle-Black Santa Clarita, CA
Join the "Bicycle Restoration Group" at http://sports.groups.yahoo.com/