Don't forget, the 2011-2012 Apex sleds have lots of engine changes, and changes to the exhaust systems.
From 2006-2010, the 121" Apex standard had 24-38 gears, the 136" Attack had 23-38 gears. The Apex RTX only in 121" had 22-38 gears. I'm thinking its more about the track length, than fuel economy.