Ok so I beat this topic to death with my buddy Mark... confirmed that yes the rates are indeed exactly the same regardless of which cord you are using. The benefit to the one from Xcel is they can monitor when you are charging your car, so their annual incentive is based on how much of your charge time fell within your committed charge time during off-peak hours. But the annual incentive is like $50...
So given that our Leaf is programmed to already charge during the cheaper off-peak hours, there's really on advantage here that I can see, other than a 14-year ROI on a $700 power cord.