As a tank, the most important stats are your mitigation ones (Defense, Shield and Absorb Ratings), with Endurance following behind. Strength (and Power) affect your damage output and consequently your threat generation, so they are much less important. So:
Defense Rating, Shield Rating, Absorb Rating > Endurance > Strength & Power
The reason why some may consider Strength and Power to be useful for Juggernaut/Guardian tanks, other than threat generation, is the fact that they contribute to the Sonic Barrier shield generated from the use of Force Scream (you gain this ability from the Immortal tree). This ability absorbs a moderate amount of damage which is dependent on your "Bonus Healing":
Sonic Barrier
Force Scream has a [50 / 100]% chance to grant Sonic Barrier, which absorbs a moderate amount of damage. Lasts 10 seconds.
Bonus Healing (from main stat) = (Strength or Willpower or Aim or Cunning) * 0.14
Bonus Healing (from force/tech power) = (Force or Tech Power) * 0.17
Bonus Healing (from power) = Power * 0.17
Hope that helps and isn't too confusing for you.
Happy tanking