Well, actually HoI2 does have seasons (winter conditions and stuff), but that's no problem. However, there is another thing that is wrong in HoI2 concerning the seasons, which is the length of night and day. Even in summer, the night is longer than day on northern hemisphere. That is because the night/day-border does shift north and south during the season cycle,. but it does not 'rotate' to make the day longer than the night during summer and vv. At the equinox (like today

), the length of day and night is equal all around the earth, so the line should be 90° vertical. This does not work in HoI2, which put day-/night-warfare at a disadvantage (or advantage for night bombing) on the northern hemisphere, regarding of season.
I really hope that part gets fixed in HoI3.