Druid vs Warrior

[Dridzt]

Ok... I see rather rough generalizations here:

Druids tank without a shield (no block) and without parry.
Their main survival traits are dodge (= avoidance), Extra Armor (=mitigation), Savage Defense (=absorption)

Death Knights tank without a shield as well (no block) but can both dodge and parry.
Their main survival traits are high stamina (= soaking), high avoidance, Blood Shield (=absorption), self-healing and a host of defensive cooldowns that require pre-planning for proper use.

Paladins have block and a mastery that works with it (mitigation), dodge and parry (avoidance) and life-saving cooldowns on "auto".

Warriors also have block and a mastery that works with it albeit differently than paladins (mitigation), dodge and parry (avoidance) and alot of utility that require reaction for proper use.

Going by each tank's distinctive survival features this is closer to the truth:
Druid = avoidance/absorption
DK = avoidance/self-heal
Paladin/Warrior = mitigation

ALL 4 tank classes at comparable gear and player knowledge are relatively balanced,
and that comes from both tanking along-side all classes in a guild that rotates tanks on all jobs,
raid leading and "using" tanks for different jobs (and poring over combatlogs that show their dtps),
and also healing tanks.

Each have their stronger sides and differences but there's no job that 1 tank class can do and another can't.

Bottom-line, do your homework on how to gear/gem/enchant your favorite class properly and stay with that, you will have no problem filling your role.