The DoT reduction on S1 is really trivial when you consider how little DoT damage tanks take compared to non-periodic damage, and how much more damage is mitigated by armor. All info below based on Rawr 12.1, rare gems, and fully enchanted.
PvP with: S1/Vindicators/Veterans, Deathblow X11 goggles, Earthwarden, Idol of Terror, Ring of Unyielding Force, Iron Band of the Unbreakable, Badge of Tenacity, and DM Card: Vengance
Unbuffed Stats: 15.6k health, 235 Resil, 35% Dodge+Miss, and 24.3k armor. 235 resil negates ~6% of DoT damage. 24k armor negates ~66-69% of physical damage, depending on the level of the boss.
PvE pre-Kara: HC 3-piece, Verdant gloves, Cowl of Beastly Rage, Neck of the Juggernaut, Slikk's, Shoulders of Assassination, Swiftpaw, EW, Idol of Terror, Treemender's, same rings/trinkets.
Unbuffed Stats: 15.3k health, 0 Resil, 35% Dodge+Miss, and 26.8k armor. 26.8k armor negates 69%-71.5% physical damage, again, depending on the level of the mob.
PvE upgraded to T4
Unbuffed Stats: 14.9k health, 0 Resil, 43% Dodge+Miss, and 33k armor. 33k armor negates 73.4-75% of physical damage depending on the level of the mob.
If your armor negates 66% of incoming physical damage, a hit for 10,000 is reduced to 3,400. If it negates 69%, it's 3,100, and at 73%, it's 2,700. Per swing, the PvP tank is taking 700 more damage, so a DoT would need to tick for ~11,700 in the same amount of time as a mob's swing timer and be undispellable for the PvP tank to take less damage.
PvE: 11,700 + 2,700 = 14,400
PvP: 11,700(.94) + 3,400 = 14,398
This scenario doesn't take avoidance into account, but since the PvE tank has 8% more total avoidance than the PvP tank, adding avoidance to the math favors PvE gear.
Edit: Increasing physical damage taken also increases the gap between the PvP-geared Druid and the PvE-geared Druid. IE, at 4k hits on the PvE bear, you'd need a DoT ticking for 17,750 per melee hit to favor the PvP bear.
PvE: 17750 + 15,000(.27) = 17750 + 4,050 = 21,800
PvP: 17750(.94) + 15,000(.34) = 16,685 + 5,100 = 21,785
Edited, Mar 13th 2008 2:18pm by AstarintheDruid