The scan I downloaded was an RGB (made up of red green blue) scan ie made up of the light primaries - you don't print with light you print with ink typically cyan magenta yellow black - converting a scan from light to ink "flattens" the appearance of the image, also some effects can only be applied to an RGB image
Converting to a usable file type prior to production is often either overlooked by "designers" or "it'll be fixed at repro" - where I'm currently working btw - an extra job which is rarely charged to the customer but if it isn't done the job will be unprintable
And I'm just being a cranky arse at the end of a boring day fixing stuff for no thanks