This is a cross-post from Google+, but I like this format better for lengthy discussion. Here is the (snipped) comment from +Gerardo Tasistro that got me thinking:
Ok, so what's got my mind working this morning is why can't magic users wear armor.
I'm working on a new explanation for it because the classic "it interferes with the magic powers" just doesn't cut it anymore.
For the game I'm working on, I'm entertaining the idea of mechanically treating all armor as the same and letting the character's individual expertise determine how effective the armor is. So you just have "ARMOR" and you describe it however you want - the fictional appearance and material of the armor is just for flavor.
Then, classes that favor close-combat can have the option to purchase abilities that improve the effectiveness of wearing armor. So maybe, the Fighter has an Armor Specialist ability that increases the amount of damage mitigated by wearing armor. This gives the player more creative freedom with describing their character while providing the classes that need the defense the most abilities to increase their survivability.
So, with this type of system, you could have a Fighter wearing Studded Leather and a Mage wearing Full Plate, but the Fighter is trained to make the most use of the armor they wear so their Studded Leather actually mitigates more damage than the heavy suit of metal worn by the Mage. Despite the fact that the Mage's Full Plate is harder to puncture, the Mage just isn't trained to move in it effectively, whereas the Fighter's Studded Leather isn't as thick as the plate mail, but the Fighter is an expert at making the most of their armor and can avoid harm with more skill.
This methodology consciously moves away from a design that favors realistic simulation and heads towards fictional effectiveness. I've always hated the fact that when push comes to shove, certain weapons and armor in games like D&D end up being the most effective so you wind up with everyone in full plate with two-handed swords. At that point, it's not about what makes your character cool but about what combination of equipment makes them most powerful. Why not separate the correlation and let effectiveness and coolness have their own spotlights?
Along with this, I'm thinking about what advantages one might have for not wearing any armor at all.