The whole resistance stacking from other games never made much sense anyway.
An item that would usually be really weak, like 5% fire resistance, suddenly is uber because its the last 5% missing to 100% resistance.
I always figured it should be one applied after the other, so for example if you wear two items with 50% fire resistance, your resistance is 75%.
Thats of course easily doable on a computer, but not that easy in tabletop, which is why D&D, being optimized for tabletop, used the system described in this thread.