The Spies have the early line on a confidential new technology being developed by VW (and some other European companies) that should bring most of their models near the 40MPG marker WITHOUT hybrid or diesel technology.
The new engines code-named the 'Super Turbo's', employ both supercharging AND turbo charging in the same engine.
Supercharging at the low end and turbo charging at higher RPM's is how the feat is achieved.
Look for the engines to start making it into cars in the next couple years...