From everything I have read in the forum and interviews with @dan, the materials and design catalog is going to be an important part of the Glowforge project. For people to get the Glowforge up and running, producing something within 15 minutes for a large number of people will necessarily mean providing for design and materials that just work out of the box. The extras given as a premium after the shipping delay are indications of the scalability of the materials catalog.
As to guaranteed or your money back, that is an interesting question. The Inventables warranty disclaimer gives quite a bit of latitude to the company; however, they do envision that some materials will not be in conformance with expectations.