A matter of etiquette. Personally, I mix mine if I'm just eating alone; otherwise I'd eat "normally" if I'm dining with others. Got some bad manners acquired over the years as well, like mixing my rice with a hot cup of coffee (topped with either fried fish OR powdered milk, whichever's available) and using ice cream/sundae as a dip for potato fries.
@ above: Not sure about restaurants selling curry, I'm pertaining about dining with other people in general (family, peers, etc.)