All stereotypes have some reason, true or not, for their existence.
Are Mexicans lazy? A good friend's father is a damn hard working cop. But she's a lazy slob. The only other mexican I've known decided to quit working all together while in the middle east.
Do blacks live off welfare? Of my black friends, one is a mathematician for the government, one is a lawyer, one is a programmer and the other plays in the NFL.
Are jews rich and miserly? I have one jewish friend and he doesn't have two nickels to rub together. His parents are wildly rich though.
But if everyone can be frank for a moment and suspend the need for being politically correct, we can all see where the sterotypes stem from.