I am also unsure whether there are preservatives in baby food jars or not. I've tried both jarred foods, and homemade, and the homemade tastes so much more real to me (like the carrots taste more like carrots, the peas taste more like peas). The jarred foods don't taste as fresh to me, and I find that a lot of baby foods are really watery... and I feel like the fruits have added sugar. I just feel safer making my own because I know what goes inside of it, and I know how it was made. It's also easier to combine foods of your desire.
I make my own baby food 99% of the time, however I do have some Heinz baby food jars in my cupboards in case we have to go out somewhere and I don't have time to make anything. We've also been to Cuba last month, and we are going to a cottage in a few weeks... and in those cases I pack the Heinz jars. I don't think they are poisonous or horrible... I just think that homemade is better in all cases, not just for baby food.
By the way, I prefer the organic Heinz baby foods over the regular ones.