It has been said before that the men of 'the story of O ' are a sad lot and the reader feels pity for O because she is left in the end. But maybe that is one of the main points why O captures the mind of the dom reader. For me, the protection instinct is a strong factor in my D/S thinking (Even if it is myself who put the girl into her helpless position in the first place). So because there is no man in the story who will protect and take care of O, the reader is enthralled to do so himself in his mind.
Satan_Klaus