[ZeroGravitas]

You can now get a plug-in Prius. So, depending on how their mpg is calculated, cleaner electricity may have an effect. The batteries are still small, but the same argument that applies to short range EVs applies, most journeys are relatively short commutes, not long distance, and so plug in hybrids can spend a lot of time on electricity alone if they are topped up every time the reach home (and/or work).