There are several ways to look at preservatives as there are several issues that need to be safeguarded against.
It would be worth taking a look at Wybauw's book on shelf life.
It discusses truffle shelf life at great length. One of the specific topics is mold inhibition through reducing the water activity. (Aw) mold needs water to grow adding some sugar variants like glucose syrup or invert sugar can reduce the water available to the mold.
It also discusses hygroscopicity of different sugars, fat content and so forth.
To my knowledge most chocolate bars don't have preservatives because they have such a low water activity.
I have seen palm oil and other preservatives in the ingredient lists on various candies. I.e. Utah truffles.
While it is frowned upon as a less pure approach to fine chocolate I'd be curious about preservative use. I would like to be able to sell in grocery stores some day. A long shelf life will e critical for that.
You are absolutely right about the shelf life, to get it in stores is my vision as well one day. I'm going to check that book out today and thanks for all your insight. It was greatly appreciated. How long have you been making chocolate