Hopefully there are others out here who play tabletop RPGs. If not, well, this is a rather specific post for a rather specific culture; its best to have knowledge of what I'm talking about before reading this otherwise it'll just confuse and upset you. I don't want you to cry.
I like looking at RPGs from a perspective that most people don't; I look at them as ways to reflect reality. The majority of RPGs use the philosophy of "Treat your Story like a TV Show, Book, or a Movie." As you can see from that link there, sometimes the philosophy is taken quite literally.
The issue with that mentality is that, well, its wrong. RPGs aren't movies, TV shows, or books, and treating it as such is generally a poor way to approach design. Why? Well, because it causes the system to become a tad wonky when faced with things that, in real life, would have a very logical and simple outcome.
I'll talk about AC soon, promise.
Take, for example, a boulder falling 20 feet on to a character. It is a 15 foot boulder; the thing is fucking huge. Let's play this scenario out with Joe the Rogue. Real life first:
Joe tries to dodge out of the way of the boulder but its like 15 feet in diameter and he's dead. Even if he mostly makes it out his lower body/leg is going to be crushed by tons and tons of stone. The boulder is going to fall FAST and his reaction time is going to have to be insane to get away with even just a leg missing. Now D&D world:
Joe rolls up his Reflex save; let's just say he misses because jumping out of the way of a 15 foot boulder isn't really going to happen. Well, then JOE takes 4d6 damage (the object fell 20 feet, so 4 squares.) Oh, wait. Its a heavy object? 4d10. 4d12 if the DM is feeling mean.
At most, the boulder does 48 damage. It has a potential to do 4. 4 is a scratch outside of the first three levels. 48 is a scratch from 10th level on. But, on a TV show or movie, yeah, no, the boulder would do nothing; people would dodge it, the hero would shake it off. Except that, well, the hero actually can't do that, so things start to feel a bit wonky and disconnected.
That brings me to AC. AC is the bane of D&D and is a stat that should be gotten rid of in the near future, because AC makes about as much sense as dodging a boulder, an arrow, or a gunshot. Why, you ask?
Because Armor, regardless of time or place, has always been about mitigating impact, not stopping it. Period. The exceptions are few if any. Kevlar vests? Well shit, you're getting hit, but hopefully not as bad since you have the vest on. Full Plate? Yeah, you're getting hit all the time; but its cushioned, and they really have to beat you in to submission or get very, very lucky.
When you design your system around AC, you hit the point where attacks are all-or-nothing; either the attack does massive, crippling damage, or it does 0. If AC is 49, and I roll a total of 48, I do 0 damage. That isn't how armor works. That really isn't how anything works.
The only time a character should be doing 0 damage is if the enemy dodged it, because that's the only time it didn't connect. If you hit the persons armor they are going to get hurt unless you're using an incredibly light weapon. But, they aren't going to get THAT hurt, and the heavier the armor the chances of hurting them big time fall drastically.
So when you get in to that mentality of "big hits or no hits" you start to make the system stupid, because that means somehow, that fullplate your character is wearing is totally letting that dudes rapier through, and not snapping it. Because fullplate works that way.
In my RPG Wayfarers, (Yes, I am Jimmy Swill.) characters have a Dodge score that indicates how hard it is to hit them, but armor absorbs damage.
In addition, armor can actually lower a character's Dodge, based on the bulk of the armor, and how strong he or she is.
You can check it out on page 32 (the 22 page) of the preview PDF.
Wayfarers is a blend of old school and new school RPG aesthetic and mechanics. Send me a PM if you'd like a copy. I'll hook you up.
BTW, I've been using the tag #rpgs. :)