I have never found a need to build roads (Interstates) in 9 years of playing.
Then either you prefer railroads or have never played a nation like Chile with huge swaths of land like its southern parts without any transport there. Much of their oil supply is down there with little to NO road or rail access. Not saying one needs to go hog wild but being able to have steady supply and easy troop access without needing air transport are both viable reasons to build roads in many areas of the world.. on the other side of the coin.. nations like the U.S. or other major nations generally don't need additional roads.. but they can still prove useful.
I won't deny your knowledge and skill as a player GI.. but there are viable reasons to build them.. although depending on your playstyle i can see how you can say they are not necessary.
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