Changes in fuel consumption affect VOC emissions by reducing refueling vapor losses and spillage. Other emissions (such as sulfates) are also affected by fuel consumption. MOVES2010a incorporates changes due to fuel economy requirements that were finalized as of spring 2010. MOVES does not model any proposed requirements.
Note that changes in fuel economy alone are not assumed to affect tailpipe VOC emissions, since these are a function of emission control technology, not fuel consumption.
MOVES2010a does include other changes to VOC emissions, namely, a change to how methane emissions are calculated reduces the VOC fraction of total hydrocarbons.
For more information on MOVES2010a, see www.epa.gov/otaq/models/moves/MOVES2010a/420f10050.pdf.