Why change the system? According to Eyonix, this is going to allow Blizzard to create items without eventually reaching a point where people could have a 100% chance to crit, dodge, etc. Eyonix also explains exactly how the new resilience stat will function.
Have I confused you with my lame explanation? No doubt! Thankfully Eyonix lays this out much better than I could, and if you like doing all the math for your character, or you simply want to know what all these new ratings mean, you should definitely check it out. For you folks stuck at work and unable to get to WoW.com, you will find Eyonix's complete post after the jump.
With the upcoming release of the Burning Crusade, we thought we would take the time to explain more on a new stat that we are introducing: Combat Ratings. These ratings are being used for any combat stat that previously was percentage-based such as: critical strike chance, hit chance, dodge chance and defense skill. Combat ratings are only used with effects generated by items and do not apply to effects that are generated by spells and talents which will continue to work the same.
The following combat ratings are currently in use: weapon skill, defense, dodge, parry, block, hit chance, spell hit chance, critical strike chance, spell critical strike chance, resilience, haste, and spell haste.
*We may introduce others at a later time.
Unlike fixed percentages such as 2% critical strike chance, combat ratings diminish in potency as your character increases in level. 2% crit is the same at every level, while 28 critical strike rating grants 4% crit at level 34, 2% crit at level 60, and 1.27% crit at level 70. This allows us the ability to create and add new and better items to the world without eventually reaching a point where every character has a 100% chance to critically strike.
Below is the level 60 conversion for combat skills:
Weapon Skill Rating 2.5 rating grants 1 weapon skill
Hit Rating 10 rating grants 1% hit chance
Spell Hit Rating 8 rating grants 1% spell hit chance
Critical Strike Rating 14 rating grants 1% critical strike chance
Spell Critical Strike Rating 14 rating grants 1% spell critical strike chance
Haste 10 rating 1% haste
Spell Haste 10 rating grants 1% spell haste
The impact on the defense skill and weapon skill systems is slightly more complicated. Many people do not realize these skills actually grant percentage-based benefits already. For example, every 25 points of defense skill grants a 1% dodge chance, 1% parry chance, 1% block chance, 1% increased chance to be missed and 1% decreased chance to be critically hit by physical attacks. Weapon skills have a similar effect for the attacker. Items will now grant skill rating rather than skill directly, and that will convert to an actual skill increase.
Below is the level 60 conversion for defense skills:
Defense Skill Rating 1.5 rating grants 1 defense skill
Dodge Rating 12 rating grants 1% dodge
Parry Rating 20 rating grants 1% parry
Block Rating 5 rating grants 1% block chance
Resilience is a special new rating which we have created to reduce the effects of critical hits against your character. It has two components; it reduces the chance you will be critically hit by X percent, and it reduces the damage dealt to you by critical hits by 2X percent. X is the percentage resilience granted by a given resilience rating.
Below is the level 60 conversion for resilience:
Resilience 25 rating grants 1% resilience
Each time you go up a level, the amount of rating needed to get the same benefit will increase. An example of the scaling involved would be the current implementation of Agility which has always worked this way in the live game, requiring more agility for the same critical strike chance as you go up in level