Seasons do have an affect on provinces. But I get what you mean, because the effects are too small to notice, generally, and armies themselves don't take any extra attrition from them.
But that is a problem that isn't unique to HatG... much of that is inherited from the base game, so I don't hold it against HatG by-itself (though I do when it comes to the base-game, because the patch that accompanied HatG sort of made the base-game odd with seasons that last a full year).