Frankly, I think that Western Union isn't in the business of caring. They make a healthy margin on every transfer, and serve a segment of the population that has a strong disinterest in having to extensively document their identity, source of funds, etc, sometimes because the funds are "dirty" sometimes because the sender or recipient isn't "fully legal", etc.

It's against Western Union's interest to extensively document everyone and every dollar that passes through their systems. I'm sure they comply with the legal requirements placed on them, but I doubt they go WAY beyond that, for doing so would not be in their best business interests