Actually red is correct pure ethanol has about 66% the energy of regular gas.
The problem with his statement is that we are running E-10, the difference in energy between E-10 and E-0 is only about 3.5%. So if your getting 50mpg, you should loose only 1.75mpg. Some cars like one of mine lost more because they don't seem to like E-10 for some reason or another.
One thing to keep in mind is if you are running E-100 you would have an octain of 122, in which you could run a much higher compression and possibly more than offset the lower energy per gallon.
http://en.wikipedia.org/wiki/Ethanol#As_a_fuel