The Foundation also had psychic powers, pocket-sized nuclear reactors, and people accurately predicting political events occurring hundreds of years in the future. Just because Clarke wrote it doesn't mean it's hard SF.
Does hard sci-fi change over time though? I'm not sure but I would imagine that pocket-sized nuclear reactors for instance were at one time plausible, if the story was written when that was a case is it hard sci-fi? Or does it cease to be hard sci-fi as our understanding of the universe changes?
