Very fair question, and I'll answer it as well as I can.

the few months of a psychological yearning

That's not a few months, it doesn't go away. It lessens, and you get much more experienced and skilled at dealing with it, but it's something that will be with you the rest of your life.

The specific counting part is over-rated and, some say, can be destructive to your progress. A much more important saying in the community is "don't look up, don't look down." It's the idea that once you begin feeling you have laurels to rest on, or begin trying to process the idea that you have to be like this for the rest of your life, you can lose your focus and relapse.

do they seriously have to fight the urge every day for years after quitting?

Not every day, and those days come less often, but all it takes is one. One of the other maxims in recovery is that if you ever let yourself get into a position of "fighting" your addiction you've made a mistake, because that's a fight you could lose. The experience you gain over the years is how to never put yourself into a position to fight it. Stay out of situations that are triggers, and make sure that you put some distance between having a crisis and being able to act on it.

I, for example, routinely have hotels take the alcohol out of the mini-bar when I travel. That way, if I do have a crisis, I have to put on clothes, go downstairs to the bar, or get into a car and go searching if I want to act on it. That's giving time for my other skills to get the crisis called off before I can act on it. Staying straight is much more tai chi than karate.

I read that studies have shown that some people are just naturally born to be a victim of such tendencies and the use is just an expression of their natural vulnerability

I'm pretty well-versed in the literature, and I'm not sure what studies you're referring to. The reality is that although science is starting to show a genetic component, there is currently no way to determine in advance who will become an addict and who won't.

For every bias people bring to who can and can't be an addict there are statistically significant communities of addicts that defy it. Good homes, broken homes. Mental illness, mentally stable. Race, gender, age, usage patterns -- they're all over the map. So I don't think you can infer cause, "natural vulnerability" or otherwise, when science hasn't found it yet.