If we want to focus on a WWII simulation, well you can establish rules saying that airplanes are not affected by terrain (since they fly). However things like forest still can provide defensive bonuses when bombing. Tanks although are very strong and do a lot of damage, they need to go around everything! (Powerful but have a limitation). Infantry could be the opposite, weak (offensively and defensively) but be able to traverse all forms of terrain.
These can be general rules and then there can be specific rules to each location.
