That's a very good question.

After seeing the day/night setting in the options, I've been agonizing over what could be wrong with my installation. Not everyone can be bothered as i was, to trawl through forums to discover the answer. This omission also detracts from the feel of the game.

Since the cost of the iPad version is comparable to the pc version and considering the other feature omissions in said ipad verion .... not good value for money.