There is a lot of perceived political freedom from people outside of Hong Kong (both people in US as well as in China - why else would Chinese dissenters travel to Hong Kong to protest?). By declaring Hong Kong has political freedom, China is forced to defend that image, both domestically and internationally. I am from Hong Kong, so I know what you're talking about, but I'm currently living outside of Hong Kong, so I know what foreigners' perspective of Hong Kong is, too.