They should be more honest and publish a combined MPG of 45.That goes for all of the other manufacturers too.
mpg is such a driver variable though, a standard test is what we have at the moment, so an equal playing field between all manufacturers. They need to tweak the test to make it realistic, but how do you define the "average" driver? Right now the current test is miles off reality - the test has the car static far more than most would be in their commute (24% of the 11 minute test run), but when moving, the driving part of the test run is far more smooth/linear than most can hope to achieve when faced with traffic lights and roundabouts.
I found the pre-start/stop figures gave a much more realistic expectation of mpg.
I can get 32/33mpg in my R without driving like a nun, mainly due to the fact that most of my driving is on dual carriageways that are busy enough to keep me down to 70mph for my 20 mile commute. Last night I was an hour late leaving work and the roads were much clearer, I did 80mph most of the way and my mpg dropped to just under 30mpg (no hardship in an R) for the trip. If I went to work in the middle of rush hour, i'd be lucky to see 27mpg. That's just the variation of traffic volume n the exact same route. When you take in account driving style and shorter journeys as well as temp/humidity variation in the seasons you've got a real mixed bag.