Yes, the US Embassy visa policy in Nigeria do discriminates because Nigeria have no working system for verifying the authenticity of documents.
And also the US is yet to recover from the post 911 syndrome that makes them think most people out to attack them. So they are very busy
flushing foreigners out of their Country, building the Berlin Wall around their Country and being very careful and strict about entry Visas.
So we Nigerians need to be aware of these facts and go to them with proper documentations as requested.