Weather has 2 effects ingame: It makes units fight differently, with or without bonuses, or with/without maluses, and it also affects movement speed, though not as seriously as terrain. So, i believe that what you mean is that terrain that is affected by the weather is not sufficiently penaltyious. And i disagree, penalties of both are significant enough that they cant simply be ignored, lest you risk messing up. Noone will fight air battles on rainy weather, or naval battles when the rainy session is going on in the pacific, unless you want a BB fleet to rush your precious carriers. Noone will risk attacking the soviets during the winter, because of the serious penalties (not to mention the bullshit bonuses the AI gets) [i mean come on Fernando Torres, 25% frozen bonus to every russian unit? have a heart!].
Winter fighting during ww1 did indeed happen, and it was horrible. Staying alive in a trench was in itself an accomplishment, and i agree that winter fighting should perhaps suffer more of a penalty during ww1 ONLY. Though i do believe this detail to be too small, so a simple event which gives a specific penalty to all land units would be better (an event that says 'winter is coming' or something, that gives an attrition modifier so you suffer more attrition casualties during winter, and during which noone would attack.
