well, it's a shortcut to come to the states as "postdoc"

Many chinese "MD"s who are serious about research did their PHD, and they came to the US for graduate schools.

Some others, with chinese MD, come to the states as "postdoc" and started working in a lab as technician first, and some proved themself to be worthy overtime. For these people, it's hard to go back and apply for graduate school entrance and the whole 9 yards with a paying job. Unfortunately, the shortcut has its pay later in the career.