The reason that defending Surprise Strike casualties are moved behind the casualty strip is that some of them may be subs, which will return fire if there are no attacking destroyers.
The rules for scrambling specifically state that you may only scramble if combat is occurs in the sea zone surrounding the island with the air base. This combat may be either a straight naval battle if defending naval units exist in the sea zone or just an amphibious attack launched from the sea zone if there are no existing defending naval units.
During the civil war the North and South used different track widths also, because front lines moved back and forth so much, there were special units dedicated to changing trackwiths as ground was gained.