Not sure what you mean here... If I add 1000 haste rating compared to 1000 of some other rating, the haste will get multiplied by those factors, but other stats will not. Doesn't this mean I get more out of Haste compared to others?

Also I'm not sure if it's common knowledge because it's tempting to assume that the 10% from Icy Talons and 5% from Unholy Aura are flat bonuses that are just added, not multiplied.

Unholy Aura is also adding 3% more Versatility, but it's not multiplicative, it's additive. Only Haste seems to be multiplicative.

I believe the same applies to Multistrike and Crit buffs. A 5% multistrike buff will just add a flat 5%, it won't multiply everything.

I think it stems from the fact that Blizzard at one point decided that different haste sources should work multiplicative, this makes a lot of sense considering WoW back in classic had quite a few negative haste sources (debuffs that slow your attack/casting speed) because otherwise you'd have weird interactions such as multiple attack speed debuffs causing you to have "negative attack speed" (not attack at all?) / "negative cast speed" (infinite cast time?).

In practice, this merely means haste rating doesn't get devalued by those buffs.

Small example: Let's say you have 100 damage / 1 second = 100 DPS baseline.

If you add 10% haste, you'll have 100 / (1 / 1.1) = 110 DPS

If you add 10% versatility instead, you'll have (100 * 1.1) / 1 = 110 DPS

Now the same with UA and IT: You now have 100 / (1 / (1.1 * 1.05)) = 115.5 DPS baseline

If you add 10% haste, you'll have 100 / (1 / (1.1 * 1.05 * 1.1)) = 127.05 DPS

If you add 10% versatility instead, you'll have (100 * 1.1) / (1 / (1.1 * 1.05 )) = 127.05 DPS

As you can see, with the current mechanics, UA / IT have no influence on relative stat weightings.

If they were additive, however, they'd devalue haste: You'd now have 100 / (1 / (1 + 0.1 + 0.05)) = 115 DPS baseline

If you added 10% haste, you'd have 100 / (1 / (1 + 0.1 + 0.05 + 0.1)) = 125 DPS

If you added 10% versatility instead, you'd have (100 * 1.1) / (1 / (1 + 0.1 + 0.05)) = 126.5 DPS

As you can see, now haste would grant less DPS than versatility.

Edit: Some more detail/different explanation:

All of this is based on the fact that similar absolute gains will result in decreasing relative gains when you have a higher baseline. E.g. in an extreme example where you have an additive 100% haste buff, you'd now only gain 1% / (100% + 100%) = 0.5% more relative haste from 1% absolute haste. If the 100% haste buff is applied multiplicative, it'd also apply to the additional 1% haste now so you'd have (1% * 200%) / (100% * 200%) ) = 1% relative haste from 1% absolute haste. At the same time all other stats would simply multiply the total damage by a certain factor that's more or less constant. Therefore 1% damage through another stat would always grant 1% damage no matter if haste is calculated additive or multiplicative.

**Edited by Hidden, 29 December 2014 - 10:01 PM.**