As a smoker, I would tend to agree with most everything that has been written....BUT that doesn't mean I like it.
When you ask for a cigarette, Do I not cry out?
When I pull the cigarette from the pack does it's brethren not mourn?
When I hand you the cigarette does my wallet not bleed?

Honestly though, I think the universal pass phrase is primarily kept in use due to fear. No one wants to say "No" because you will never know who and when you will have to borrow a cigarette from someone. It is about building connections. I have found these connections also extend past the cigarettes themselves. I have gained valuable information and assistance in the business world from other smokers whom I met while smoking outside some building or another. Perhaps there is a bit of tribal or clan mentality that goes along with smoking, especially since it is becoming more and more frowned upon.

Also, let us not forget proper (but not required) etiquette when two acquaintences go through the ritual.:

If you borrow a smoke from someone you know (not know well, just encounter semi-frequently)and you do it on a basis that is considerably lop-sided in your favor. It is considered good manners to buy that person a "thank you" pack as a means of showing appreciation for all the times they saved your ass. This also insures the giver does not feel short changed and will not mind giving you smokes in the future because they can depend on you to keep things honest.