Optimisn, perhaps.
Top Gear looked at a recent reborn US muscle-car not so long ago and they noted a large disparity in claimed horsepower and actual horsepower. I think they even tested it. (I don't remember what car it was as I'm not that much of a fan of US muscle cars - I prefer European sports cars.)
I was going to post "I suspect testing methods have changed" but that's something I would expect TG to mention. Maybe testing methods are different: they've never, to my knowledge, mentioned the US and the UK gallon is a different size. Different enough that MPG can be quite different.
Wade.
