LOLIt actually matters a great deal.
In a competition between:
a) large numbers of cheap incoming anti-ship missiles
B) a few expensive defensive SAMs
Guess who is going to be the winner?
in real world, the USN would sail with an assortment of missiles needed to accomplish the mission (irrespective of what's the cost of said missiles),
or the USN would keep off = wouldn't sail into an area where it could meet a hail of your "cheap incoming anti-ship missiles"
(the US Military has aerial assets, too, you know)