That's why I can't figure out why Kunsan has block 30's and 40's and Osan has block 40's only
Osan has A-10`s along with the F-16 Blk40 - great from a logistics point of view
The most important factor I believe lie in the mission the base or wing has. Multiple tasks - multiple planes. In a perfect world you would only have 1 type of aircraft per base, but in todays changing threat environment you need to come prepared for most if not all eventuallities. Thus you get bases with different types of Vipers or different types of planes.
366WG is another good example; F-15E`s, F-16C Blk.50`s and B-1B`s
As for the 8FW at Kunsan, the 80FS flies Weasel missions with blk. 30`s while the 35FS flies the ground attack with their blk. 40`s.