I have wasted over a year in actual time played to World of Warcraft on one toon and I had four 90's. So this addiction for finding better loot is strong with me.

I don't know, but if you want a cure for obsession, play Final Fantasy Tactics putting move-find-item in all your party and walk over all squares of the game.

lol,
no more looting for me after this.

Loot games work like this.

1.Start out as a zero
2.Slowly become a hero
3.Get more gear to feel more and more heroic
4.See other heroes and get motivated
5.Get even better gear and become a greater hero etc etc

Well actually its very much tied to the gamplay too. If a loot based game has loot thats purely only shiny and that loot has not much impact in gameplay the novelty will die quickly.

For eg Diablo3. You find a bow that give faster attack speed and critical chance. Also has a fire effect with bonus to a certain skill. This directly affects your character and will already make you feel heroic and not just the new look of the weapon. The new drop will affect your stats permanently and even the way you will play from that point onwards. Maybe you would have used certain skillset that depends on ranged bombing of some sort, now with a faster attack speed you try out a whole different set of skills and method of play.

So yea its basically a motivation to keep you improving.
Loot system is like life in general. We always want to achieve perfection.

Every male wants to be Adam and female want to be Eve. There is a virtual human that is the ultimate role model. What that so called Adam and Eve is capable of we dont know.

Same way we dont know if better and better loot will make us perfect. Maybe perfection was reached 20 item drops ago but we are still looting. So yea there is no real gauge. the gauge is very much in our experiences and desires.

So basically that is whats good loot progression.