The US is just as bad as China and Russia. Include the UK too (tracks and cycling in particular).
The difference? China and Russia are super centralized countries that can organize state doping. The US and the UK are more federal and highly privatized countries; their doping programs are done through private clinics, sport centers, universities, "camp" (Nike Oregon). It's not as organized as Russia, but probably as spread. Which makes it harder to detect. The number of British medals at London 2012 for example was outrageous. But "China bad"...
Other difference, the US have more influence on international institutions and regulations. They can act as the policemen in the backstage.