Well, for one I don't consider myself a hardcore gamer or negative nancie. I don't think my last one or two posts were neither immature or threatening either. Though I know I was ranting, regardless, I just felt the direction of the game was heading down wasn't great. [Personal Opinion]
As other posters have argued, having these damage types, mundane and magical "Arcane", might not be enough to differentiate how spells work and how some creatures work. As Frogboy's major inspiration is Master of Magic, in MoM the spirits or whatever they are called have "Corporeal" as one of their abilities. Meaning, physical weapons do only half their damage against this spiritual creature. The same applies to Elementals and how it will both look stupid and lacking if you cast a fireball at an Ice Elemental for it to only receive the same damage if you threw it at anything else. In the end they are resistances and that can't be ignored. Certainly if I'm fighting against a Death Dragon in E:WOM, any physical weapon or magic that is enchanted with death won't do a damn thing to it, hell, should even heal it as an effect lol.
As someone described earlier, tagging as in Dominions or whatever it is called should be the way to go in terms of providing these logical resistances for units.
I do agree with you Frogboy in that having to reequip your entire army to another resistance is going to be boring, but I think looking at it that way is very narrow-minded. Who's to say in the final product, making your entire army almost-immune to one resistance type is an incredible gamble and one nigh-impossible to reverse because you are in a large-scale war whereas you can't be pulling armies from defenses and offensives? Also, as someone mentioned, why would everyone be compelled instantenously to reequip their armies to another resistance type because they ran up against something different. My point being, I'm not necessarily advocating millions of resistance mechanics, but as Vieuxchat mentioned, having one resistance type for everything just isn't feasible.
Since you played Dragon Age: Origins, you know there is resistances in the game as well as different damage types like acid and frost. Their damage types always add up, but so do resistances, in very small porportions. Truth is, in Dragon Age: Origins, enchanted weapons give you a minor boost but nothing major that really influences the battle, lest someone has their resistance lowered in something.
I think this argument is also being exaggerated quite a bit, but some of us such as me I conclude feel having just one magical resistance and lack of damage types will destroy any organized rock-paper-scissors formula. Thus, the game will be really simple and straightforward unless we add these tags for certain creatures and what's been discussed. Although as someone said, I guess your not looking for fundamental discussion but fine-tuning. Regardless, I will end up playing it and still contributing because I know I will enjoy it for its other features in a grand scale.