I think what is important to remember is although us MK7 owners aren't saving too much fuel over the MK6 model what we are saving on is road tax.
If you look at a MK6 GTI the annual road tax is £200, on the MK7 GTI it is £125, so a saving of £75. That saving buys around a tank of fuel, around 56L if you pay 133p per litre.
So over the course of a year you gain a 'free' tank of fuel or around 400 miles compared to the MK6 GTI.
J