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Needs suspension too, otherwise the crimped part of the downtube serves no purpose, surely?

(I realise it's not crimped, but I don't know what it's called.)

The curved downtube is to ensure that the fork crown doesn't hit the down tube if the bars are turned more than 90 degrees. Naturally, this is unlikely to happen when you're riding, but may well happen in a crash, and the last thing you want is to end up dinging the downtube with the fork crown.