I thought that derivative copyrights only applied to work that required intellectual effort, such as a translation (for a book) or reinterpretation (for a song). The physical act of scanning doesn't seem like it should count.
Newton's written notes may have required even greater care, which one could possibly argue would constitute unique intellectual effort.
IMO copyright should not be granted on 'mechanical' reproductions no matter how much sweat is produced on how many brows.
Would Cambridge Uni really not digitise it's manuscript collection if they could not directly commercialise it?
Maybe a new 'right' is required?