I'd say that the American libertarians, as a movement, have mostly been "captured" by monied interests who are cynically using the libertarians to promulgate policies beneficial to those monied interests - with no regard whatever for whether the policies are also beneficial to the libertarians being used.
The American libertarians, as the mouthpieces of corrupt monied interests, mostly wind up speaking out in favor of the right of employers to pay as close to nothing as the labor market will bear, to provide nothing in the way of benefits, etc... to make a 'race to the bottom' in terms of compensation for labor. Most of them aren't employers, and would not benefit at all from such policies; in fact most of them would do substantially worse under those policies. On the liberties that they would actually benefit from - free speech, freedom from surveillence, freedom from unreasonable search and seizure, freedom of religion, right to fair and speedy trials, and so on.... they are silent because agitation in favor of *those* liberties would not serve those who have captured their movement.
The movement in Hong Kong is much younger, and this kind of "capture" hasn't yet had time to take place. Further, with the Beijing government much less responsive to speech in general and the Chinese labor market already deeply buried in that same kind of 'race to the bottom' for compensation, it's not clear that that kind of capture would be as beneficial for the corrupt money in China as it has been for the corrupt money in the USA.
So, American Libertarians are Libertarians, who believe in the free market, including believing that the free market will be enough to raise wages to sustainable amounts without the need for government intervention (which, ironically, is how China wages have increased from practically nothing, to relatively good wages they have now), and Hong Cong Libertarians are not libertarians, but are pro-democracy socialists?
Ah, so the difference is that Hong Kong libertarians actually have gripes with regards to freedom of speech and assembly, and American libertarians are free enough, and should shut the fuck up about it and not protest (or, put another way, America should become like Hong Kong in regards to libertarian protestors). Okay.
Ha ha. You think China's wage growth has nothing to do with govt intervention?
http://en.wikipedia.org/wiki/Minimum_wage_in_China