I would add that when you're talking about rewards, you're often talking about financial crimes, and the amounts are very large. They overcome the fact that the person who blows the whistle in those situations is basically going to be unemployable in that industry, forever, after that.
However, if you're talking about government, it's a little harder. Offering somebody a little bit of money to fix problems might work in some circumstances, but it wouldn't work in all. I think we have to be thinking more about how to remove the stigma of speaking up inside the public service.