It's a simple bit of knowledge that a lot of countries worldwide have understood years ago: Just because another country has allowed the use a specific GMO does not mean that you have to agree with their decision and/or their risk assessment.
Now this knowledge seem to have reached the USA as well, and in the New Scientist a USDA official is quoted with the following: "Unless international developments in transgenic plants and animals are closely monitored, USDA could be unaware of potential threats that particular new transgenic plants or animals might pose to the nation's food supply."
The reason: So far most commercialized GM crops were developed in the USA, and went to the US approval system before the US wanted to export them with as little hassle as possible around the world. But now other countries like China are developing their own GM crops and products, and this leaves the USA at the receiving end.
But hopes that this would make the USA change their mind, drop their WTO complaints and join the Biosafety Protocol are probably still in vain nevertheless.