The EPA uses the amount of energy consumed at the wall, and does not rely on the on-board meter, which only displays how many kWh the battery accepted.
A Leaf thread showed a charging efficiency of 75% on 120v, and 85% on 240v when measured with a kill-a-watt meter and comparing to the on-board figure. Part of the extra loss associated with charging at 120v is that various cooling fans run while charging, and it takes much longer to charge at 120v. There is also more loss due to heat in the charging cable since lower voltages spend a greater proportion of their energy overcoming the resistance in the wire.
The 120v charging efficiency of 75% agrees with what I'm finding on my Prius plug-in. I'm seriously considering selling my beloved TSX and going with a Leaf, but I'll hold off and see what prices do when the upcoming Volt is released.