I don't think anyone needs to justify buying such containers. They save considerable packaging waste by allowing people to bring food to work or play that is sold in larger, multiple-serving packages, rather than in individual servings. They also save on the often ridiculous use of plastic wrap and foil to store food for a day or two in the refrigerator. If Zip-Loc's food storage containers are just as durable as the type made by Rubbermaid and Tupperware, and cost less, more power to them. I agree with Vanessa that, at 50 cents apiece, the cost of the Zip-Loc containers should discourage most people from throwing them away.
Durability is a crucial element of waste prevention.
Johnson Wax' promotion of their Zip-Loc containers as disposable is simply a step in the wrong direction. It's hard enough to make progress in waste prevention without manufacturers producing products that move us ever closer to a disposable society. It serves four counties in Washington State, including much of the Seattle area. Ultimately, I think that you will find info that I should add to the site, though I hope that the site is helpful to you to begin with. I don't know.