Here's the thing with active combat.
From a Developer's perspective, physics is really really hard to integrate into a system where everything you do needs to be uploaded to a server and then distributed to everyone who can see you. Why? Because of the dynamic interactions and scripting that needs to take place. Active Combat is really just annoying to other players.
Since you're bringing up Fable so much, let's say that Lionhead just announced that they're making a Fable MMO with everything a Fable fan could ever dream of. Active Combat, Physics, the works. How hard would that be to achieve, and how would it differ from conventional combat systems?
I'm not sure how WoW scripts their hit and misses, but all games that have recoils (such as Fable and fighting games) have one thing in common. They use either Hitboxes or Colliders, as they're sometimes known. Basically, when Collider A (Ryu's fist, for example) hits Collider B (Ken's head), you have a specific scripted event for exactly what is going to happen. Decapitations and Disarms in Fable/Fable 2 work the same way. It's scripted. If you have two scripted events happening at the same time (two people slashing at the same target, for example) then things can get pretty messy, and a mess is something that you definitely do not want in an MMO, which brings me to the Annoyance part.
So say you're Super Awesome Melee DPS Guy, and you're in a Raid. With 45 people hacking at the same guy, you're going to be pushing him all around the room. How are the Melee DPS going to do their job when they're chasing their target all around the room? Why must the Ranged DPS and Spellcasters reposition themselves whenever they're out of range again? How are AoEs going to be effective if the target will simply be blown out of the targeted area? MMOs are based on things not moving, and watching bullets, arrows, and fireballs auto-home in on their target is just stupid, which brings me to the last part.
The Player Base is not here to play Oblivion. Yeah, that one RPG where everything had to be Aimed. Could you imagine the fast-paced combat of Fable happening in an Oblivion format? It would be impossible. Raiding would be a horrendous experience if everyone had to aim their fireballs and rifles. As said before, it really just does not work. Also, the Hack and Slash method does not work for MMOs, because people like to strategize. The Legend of Zelda has no multiplayer, and the Fable Series limits Multi to two at a time. Why? Because bigger parties require coordination. And in order to coordinate, you need to have a reference point for how much damage everyone is doing, and when you're target is going to die. Hence the numbers and Health Bar system. It all goes back to the table top D&D games where eveyome would see the dragon, talk it out, then proceed to kill it. If the Dungeon Master throws out something unexpected, then the party simply re-evaluates. There is no pause button in an MMO, so everyone needs to be coordinated in a way that is not possible to do with current "non-conventional" systems.
Tl;dr: Doesn't work. Don't worry about it, go play Rift or GW2 when it comes out. Both have very inventive Combat systems, it seems.
From a Developer's perspective, physics is really really hard to integrate into a system where everything you do needs to be uploaded to a server and then distributed to everyone who can see you. Why? Because of the dynamic interactions and scripting that needs to take place. Active Combat is really just annoying to other players.
Since you're bringing up Fable so much, let's say that Lionhead just announced that they're making a Fable MMO with everything a Fable fan could ever dream of. Active Combat, Physics, the works. How hard would that be to achieve, and how would it differ from conventional combat systems?
I'm not sure how WoW scripts their hit and misses, but all games that have recoils (such as Fable and fighting games) have one thing in common. They use either Hitboxes or Colliders, as they're sometimes known. Basically, when Collider A (Ryu's fist, for example) hits Collider B (Ken's head), you have a specific scripted event for exactly what is going to happen. Decapitations and Disarms in Fable/Fable 2 work the same way. It's scripted. If you have two scripted events happening at the same time (two people slashing at the same target, for example) then things can get pretty messy, and a mess is something that you definitely do not want in an MMO, which brings me to the Annoyance part.
So say you're Super Awesome Melee DPS Guy, and you're in a Raid. With 45 people hacking at the same guy, you're going to be pushing him all around the room. How are the Melee DPS going to do their job when they're chasing their target all around the room? Why must the Ranged DPS and Spellcasters reposition themselves whenever they're out of range again? How are AoEs going to be effective if the target will simply be blown out of the targeted area? MMOs are based on things not moving, and watching bullets, arrows, and fireballs auto-home in on their target is just stupid, which brings me to the last part.
The Player Base is not here to play Oblivion. Yeah, that one RPG where everything had to be Aimed. Could you imagine the fast-paced combat of Fable happening in an Oblivion format? It would be impossible. Raiding would be a horrendous experience if everyone had to aim their fireballs and rifles. As said before, it really just does not work. Also, the Hack and Slash method does not work for MMOs, because people like to strategize. The Legend of Zelda has no multiplayer, and the Fable Series limits Multi to two at a time. Why? Because bigger parties require coordination. And in order to coordinate, you need to have a reference point for how much damage everyone is doing, and when you're target is going to die. Hence the numbers and Health Bar system. It all goes back to the table top D&D games where eveyome would see the dragon, talk it out, then proceed to kill it. If the Dungeon Master throws out something unexpected, then the party simply re-evaluates. There is no pause button in an MMO, so everyone needs to be coordinated in a way that is not possible to do with current "non-conventional" systems.
Tl;dr: Doesn't work. Don't worry about it, go play Rift or GW2 when it comes out. Both have very inventive Combat systems, it seems.