The Earth orbits the Sun at a slight angle, rather than "rolling" on its side. Everyone is familiar with this: it's what causes summer nights to be longer than winter nights. (Adjust as appropriate if you live south of the Equator.) As an extreme example, at the North Pole the day is exactly as long as the summer, and even in parts of Scandinavia it's not dark for more than a couple of hours a night in the summer.
Are we going to model this? As I see it the decision is based on:
- amount of time to program the feature.
Well, it's a fairly simple calculation, and assuming the earth orbits the sun already then all the code that needs to be written already has been, it's just a case of reusing it.
- gameplay issues.
Assuming that you regard fighting during the day as desirable and fighting during the night as undesirable, this makes bases in the Southern Hemisphere slightly better than bases in the Northern Hemisphere at the beginning of the game, which flips over as you approach June (ie midgame in the first two games) and then flip back again as you approach December (usually the end of the game, or even after). If this is undesirable you could just randomize the starting date of the game.
- feel of the game.
I think this is either positive or not contributory: people who notice it will think "Wow, that's cool", and people who notice it won't care either way.