Not every one, no. The biggest problem is that I spend most of my driving stopped at traffic lights or in expressways turned into parking lots like they do around here from about 3:30 until 7:30PM and from 7:00 to 9:00AM. Average speed since I got the thing has been 29.3 mph.
What about on the freeway?
The Z06 has a 7 liter engine. The only way to get more power out of an engine is to make it able to burn more fuel per unit time, and it uses a fair amount just sitting. Freeway is about 27 - a little more if you really nurse it. Regular C6 coupe burns regular gas and gets 17 town 28 highway.
27mpg for 505HP 427 small block is nothing to sneeze at.