Mark B's (One of the finest builder's I've ever known, and who I wish that some day he'd make it backing to the building fold.) frames built for Ken Carpenter were the extreme of stiffness, but for a guy like Ken you need stiff. So the "right" stiffness for Ken was as stiff as possible, where as Sean liked a noodle. I've never built a bike for any pros, but I have worked on a ton and built their wheels. The one thing that seems to come out every time is that different riders prefer different things. Very few pros really care very much what they ride as long as it has the preferred ride characteristics and someone writes a check every time they ride it. At the pro level it's the motor that gets the job done. There are nice things like index shifting and STI/Ergo shifters that allow the motor to concentrate more on putting out horsepower.
Eddy started the race by being one of the first pros to train the way pros train today. Training before and during Eddy's time was a lot of miles, lots of sleep, and lots of carbs, and maybe a little cyclecross in the Winter. Anybody who has been a competitive athlete in the last 20 years knows that just doesn't cut it anymore. Lot's of sleep is just as important, but putting in miles doesn't do much unless you're varying your workout and thinking in terms of target heart rates and peaking. Eating is much more regimented and regulated than in the days past too. Cyclocross has been replaced by going to some place like Santa Barbara and continuing your strictly designed training program and preparing for the up coming season. Greg Lemond said it ten years ago "There are a dozen Eddy's in the peloton today." Today that number is much higher. The main reason is the training. After Eddy they figured out that you can improve the motor much easier and to better effect than changing the bike. That is not to say that Mario or Frankie could jump on a 25 year old Cinelli with period parts and still be competitive at the level they are. I do think you could put them on a 25 year old Cinelli with modern parts and you wouldn't see much of a difference in their placing on the world rankings.
enjoy,
Brandon"monkeyman"Ives