Also, note that there are two types of manufactures made in China: those meant for export to places like the US and Europe, and those meant for Chinese and/or third world consumption. Any goods you buy that are meant to be bought from locals will be of a lesser quality; any goods you buy that are meant to be bought by foreigners is the same quality as you would get in the US (if it's not counterfeit) and will cost exactly the same amount that it does in the US -- China puts an "export" tax on items that are meant to be sent overseas. Case in point: I bought my Macbook last year in Shanghai, and paid the same amount I would have paid in the US, even though it was made in a factory in Shanghai. I could have gone to the electronics market in Shanghai and bought a (counterfeit) Windows machine for the equivalent of $200, but it would have been lower quality everything.
The frames you buy in the US are shipped from the factories to the US... there is no Chinese market for them. So if there is a specialty shop in Beijing that sells top-quality bikes, they are likely paying the export price from the factory in order to get those frames.
Also: if you are getting something like a 70% discount on anything name brand in China, it is almost definitely a knock-off.