According to the endocrineweb.com website, type II diabetes has a significant herediatry/ genetic component (that's why it's much more common in some populations, such as Native Americans), though obesity is also a factor.
"Type 2 diabetes tends to be fairly hereditary in contrast to type 1 diabetes. Approximately 38% of siblings and one-third of children of people with type 2 diabetes will develop diabetes or abnormal glucose metabolism at some point...Studies with identical twins showed that 90-100% of the time when diabetes developed in one it would also develop in the other compared with 50% in type 1 diabetes."
Researchers suspect that while some may be genetically disposed to Type I diabetes, environmental exposure plays a stronger role than in Type II. One factor under consideration is the effect of infant formulas; the TRIGR study is investigating this possibility.
I'm not sure where the studies are published, but the inheritability of Type II diabetes is a generally accepted fact in endocrinology, found in any basic textbook on the subject.