Not sure what would be gained by Apple saying "screw you" to China
They'd be banned from selling in China, and the Chinese people would not be any better off than they are today. If Apple should effectively ban themselves from selling in China why shouldn't Microsoft also be banned - the only reason they don't get these sort of "requests" from the government is that Microsoft doesn't have the ability to limit what applications are installed on Windows.
Barring Chinese from buying Windows PC/servers would hurt China a lot more than barring them from buying iPhones. In the short run, at least. Probably the reason the US doesn't do anything aside from making disapproving glances in Apple's direction is that they know China is quite easily able to come up with its own alternatives (already has done so for phones, with their non-Google versions of Android) and those alternatives might someday compete outside of China and take market share away from companies like Apple, Microsoft, Facebook, Google, etc.