Why AC instead of physical resistance?

[pampl]

Another pie-in-the-sky game mechanics question from pampl I understand the point of having a number which represents completely avoiding an attack, but I'm curious about why that number should be A) tied to physical damage reduction and B) partially be a function of armor thickness. The alternatives as I understand them are:
A) The system fizzix implemented (IIRC), and that crawl uses, where evasion and damage absorption are separated. This is nice for simulation reasons because it intuitively makes sense the two are separated, and nice for gameplay reasons because it lets you have nimble rogues and mages who can dodge attacks but aren't good at reducing the damage when they're hit. It also lets you treat spell and breath weapon accuracy like other projectiles without having their damage reduced by armor. The downside is that it still treats physical damage differently than all the other damage, which arguably doesn't make sense in the world of Angband where physical damage is relatively unimportant (though still the most common)
B) Split evasion and absorption as above but treat absorption like any other resistance. This is more consistent, but if the resistance is on all armor then it becomes meaningless, and if it's not on all armor than some non-magical armor becomes literally useless. There's also the problem of someone just wearing plate shoes (for example) to get physical resistance then wearing light armor everywhere else. It's also less granular than AC is for damage absorption - it would eliminate the differences between, say, chain and plate or robes and leather.
C) Treat physical damage sort of like acid and have it hit a random slot. If that slot has the HEAVY_ARMOR flag then the damage is reduced by 50%. Avoids the shoes problem, and makes more intuitive sense, but still isn't granular so it collapses the differences within heavy armor and non-heavy. That stuff all becomes just flavor. Also it's a hidden rule that players wouldn't immediately pick up on unless we add new combat text ("The orc hits you in the foot!")
D) Use additive resistances and make physical resistance a category like any other. I'm not a big fan of additive resistances, but this is a case where it seems like the best choice. It offers granular distinctions between armor, it's consistent between physical and other damage, and it's an immediately understandable game mechanic. Is there a problem with it I'm missing?

PS: this is a theoretical discussion; I'm not trying to demand massive changes in Angband.