>>>That sort of economy is achievable with a ten year old petrol VW Polo, *without* all the heavy complex hybrid stuff
Unfortunately it would fail the updated U.S. LEV-II standards (too much NOx). The reason MPGs have been dropping in newer cars is because the engine is being tuned to run richer to pass emissions tests.
The best petrol car right now that can pass these tough regs is the Civic HF at 45mpg. And the Chevy CruzeEco at 44. That's very close to what the Civic and Prius hybrids do.