Insiders, Outsiders, and Ethnic Jokes

My father is funny. He'll entertain at a party with jokes about Bengalis sitting around philosophizing and drinking tea in undervests while the rest of India slaves away at outsourcing. He pokes fun at his own inadequacies as a Bengali husband. The shared laughter at Dad's perfect timing and delivery bonds his all-Bengali audience together as they call out for more. Okay, they're ethnic jokes, but nobody (as far as I know) has ever taken offense. Yesterday, however, my sister received an ethnic joke that did cause offense. It had been forwarded many times to dozens of Anglo-Saxon-ish names:

For centuries, Hindu women have worn a spot on their foreheads. We have always naively thought that it had something to do with their religion. The true story has recently been revealed by the Indian Embassy in Washington, D.C. When these beautiful women get married, she brings with her a dowry. On her wedding night, the husband scratches off the spot to see if he has won either a convenience store, a gas station, a donut shop or a motel in the United States. Just thought you would like to know.
We're puzzled about (a) why it was sent to my sister (the first Indian name to be cc'ed); (b) why our minority community is now becoming the brunt of majority humor; and (c) if there could be any context where this joke might be received as faintly funny. Anybody up to hazarding some answers?