
Fenier, I'm not doubting your post at all but I would be interested to see any hard data which supports the numbers you are giving out. As far as I know, the only solid conclusions in regard to bosses I have seen come from beast lore on Maexxna, and basing everything on one data point seems a bit questionable to meespecially as this is actually extremely difficult to confirm in terms of datagathering.
Perhaps testing has been done that I haven't run across, so I would love to see it.

Test Case 1:
Mob: Infesting Jormungar
Zone: Storm Peaks
Mob Type: Normal
Base Stats:
Melee Damage 421  587 Damage
Demoralizing Roar  Base Value of 411 AP
Melee Damage 362  528 Damage
Variance in minimum hit  14%
Variance in maximum hit  10%
Demoralizing Roar  Talented Value of 575 AP
Melee Damage 339  505 Damage
Variance in minimum hit  19.5%
Variance in maximum hit  14%
Test Case 2:
Mob: Azure Mage Slayer
Location: Heroic Violet Hold
Mob Type: Elite
Base Stats:
Melee Damage 569  792 Damage
Demoralizing Roar  Base Value of 411 AP
Melee Damage 489 713 Damage
Variance in minimum hit  14%
Variance in maximum hit  10%
Demoralizing Roar  Talented Value of 575 AP
Melee Damage 458  681 Damage
Variance in minimum hit  19.6%
Variance in maximum hit  14%
Trash showed a 14% variance in maximum hit and a 19.6% difference in minimum compared to the verified values above of 12.5% and 17.1%. Even as this seems to be the case in this test, your looking at a less then 2.5% difference between how 575 AP effects the Raid Boss compared to normal trash.
Raid Boss:
Maexxma Base Values are:
19,547  26,828 Damage
With Full Roar I can confirm the values of
16,220  23,501 Damage
This shows a minimum hit difference of 17.1%
This also shows a maximum hit difference of 12.5%
This is an averaged decrease in melee damage of 14.8%
Base Damage: 19,54726,828
Base Shout: 1716924450
Shout 1 / 5: 1697824259
Simply by applying Shout at base rank you reduce the maximum hit of the Spider by 8.9% and the minimum hit by 12.2% or 10.55% averaged.