Most schools follow the course of action outlined by Chicago's GSB:
Bangladesh, India, Pakistan, Sri Lanka:
Applicants must have completed a master's degree. One year of a two-year master's program is not sufficient. The B.Com., B.A., B.Tech., B.Eng., or B.Sc., or other similar degrees alone are not acceptable.
Hope it helps,
Do u mean that B'desh, India, Pakistan undergrads are not considered for PhD in US schools?