| Personally I think this is a very naive view. In all honesty, I'm a bit tired of all the conspiracy theories.
Who would lose billions of dollars per year. Lilly, Novo Nordisk? Yes certainly these guys would feel a major hurt, financially.
But this would be an absolute windfall for whichever company could come up with a treatment of this nature. Guess what, the next big winner will be the group that finds a way to prevent the disease all together.
Take a look at some of the therapeutic agents for orphan diseases. They sell for hundreds of thousands of dollars. Although transplants may not be that expensive (then again they very well could be given the fact that they offer something no other therapy can), they certainly will not be cheap.
The reason it hasn't been cured yet, is because it's a rather complex disease to cure. The other reality is that it woudl take years for a cure such as this to become practical. The number of cells that are required for a single transplant are huge. Now imagine trying to scale this up to cure all the diabetics. Not an easy or quick task. Sales of insulin won't plumet overnight because of this.
Think about how much money insurance companies, business, and the federal goverment lose every year due to complications of this disease. Not curing it, has a much more significant financial impact on many more people than the few companies that would be hurt by someone finding a cure.
Will we see a cure in my lifetime. I hope so, but I really have no clue. But I know for a fact, that it won't be because lilly and other insulin manufacturers would lose money, and whoever does come up with the cure will be very, very rich.  | 
