I don't think it has much to do with being American. Cycling worships the greats no matter where they are from (take Pantani for example). It's an extremely tough sport with people who historically came from tough backgrounds. When a cyclist gets badly injured and you see them cycling on - it's because they have no other choice. They will lose their livelihood if they don't. None of this excuses drugs but it might explain why people identify with and often admire them no matter what country they come from.