This image represents the gestalt principle of continuity. The font is all the same except "amazon" is bold. The eye is directed from the a to the z and the line also forms to make a smile. I think this is a very effective way to carry the eye from one letter to the next and to also have the name stand out more than the ".com". There is nothing extraordinary about the typeface but I think the simplicity of it really does elicit a positive image for the company.