The split is political. It can be quite inefficient: When the Airbus A380 was in development, the non-unified production caused severe delays because only at assembly did Airbus discover that the electric cables are not long enough to connect the different plane parts[1].
I'm trying to remember where I read about Airbus designing the plane in two different places and when they built the thing it turned out that one place was using version X-1 and the other X and that caused really subtle problems with alignment.
I'm sure it was Airbus but I can't find the article.
I'm sure it was Airbus but I can't find the article.
EDIT: Found it http://calleam.com/WTPF/?p=4700
Offtopic but the "Catalogue of Catastrophe" is a damn good read http://calleam.com/WTPF/?page_id=3
Basically a "why things failed/cost a fortune that shouldn't" list for large projects.