I believe they developed the curved array to presevse some hearing. Not sure exactly why since I really don't think a HA would do that much with what is left. 
Heres an article on the nucleus hybrid array which would be used for people with high frequency losses. (mine was a reverse slope so even if it had been available 20-30 yrs ago it would not have been of much assistance to me)
http://www.ohsu.edu/nod/documents/week3/Gantz paper.pdf
