The explanation I got on the Rome hit wasn't that it was high, it was that the hit was made 2 seconds after Horton played the puck, and that fell outside the 1.5 second range for post-playing the puck contact. So really, the only thing that made Rome's hit illegal was that his reaction to Horton playing the puck was .5 seconds too late. Had the hit happened 1 second after he played the puck its probably not even a penalty.
What I was told and I believe it was a Bob McKenzie utterance. First the hit was considered legal as you mention it was the timing. TSN ran it frame by frame and McKenzie said it was 27 frames from the moment the puck left Horton stick to the first contact by Rome. I'm told ( By McKenzie ) that 27 frames = 0.9 second