I suppose science fiction should be able to explain away all its marvels, while fantasy's magic is less analysed. Still, there are plenty of technologies "indistinguishable from magic" even in hard science fiction, and no few fantasy writers have discovered that putting limits on their magic, establishing laws, made the situation more exciting, not less; and that is essentially applying the scientific method (for me, the touchstone of the difference) We've seen dragons, trolls, griffins, werewolves and vapires in major or minor roles in SF, with time travel, nuclear fission and public transport in fantasy: either technology has attempted weather control, mind control, genocide and social disruption or uniformity.
Someone back in the Campbell days suggested that SF was essentially democratic, while, in fantasy, the hero would always turn out to be the undiscovered son of some noble or another; another suggestion was that SF looked towards an improving future, while fantasy lived in a dark age, after the downfall of a previous, higher civilisation, who's ancient relics hung about for good or evil to stumble over (excuse me; go on mighty quests to discover) Anyone here can point out exceptions on both sides to either of these conditions. More than anything else I suspect, the difference is in the writing style as much as in the content - SF readers expect explanations, fantasy readers would prefer not to have them, but like the feeling that they exist somewhere. (Whee, vast generalisation)