I think the key difference is that the AI can convince the person. You might say that a person is fully competent to judge the Friendliness of the AI based solely on the code, and yet not want a (superintelligent) AI to get a chance to convince him, as superintelligence trumps intelligence. The difference is whether you have a superintelligence working against you.
AI Box Experiment Update #3
Tuxedage (AI) vs Alexei (GK) - Gatekeeper Victory
Tuxedage (AI) vs Anonymous (GK) - Gatekeeper Victory
I have won a second game of AI box against a gatekeeper who wished to remain Anonymous.
This puts my AI Box Experiment record at 3 wins and 3 losses.