I think it's more about how you drive.
I usually don't drive my 23reg Crosstar I bought a year ago, very far. Just local shopping a few times a week and visits to my golf club, six miles away, up to three times a week.
Consequently, when it's cold, the engine is required to provide for the heating system. So given the short journeys I do, it's on for most of the time. It's also on when I let it sit on my drive with it running, if the windscreen needs de-icing before I set off.
Currently, I'm getting just over 40mpg. I'm not bothered, for 27 years I had CRVs where with this sort of motoring, the cars returned about 23mpg.