It has been my experience that the Toyota Prius is right on the EPA sticker estimate. I now have my 2nd with the same results. I find it interesting that the new Ford C-Max is trending far below the sticker estimate of 47/47. It looks more like the high 30's. Now, that would really be a bummer.
I would say it's driving style. My Toyota Prius C gives immediate feedback, and yes, if I ease on the accelerator (but accelerate on fuel, not EV), it's not hard to beat the ratings. What is hard is to do it continually, i.e. it requires self-control and planning (leave 3 minutes early, so you don't feel the pressure to hit the pedals).
I have been mpg-testing my 12 Imp cvt for a year, now. It has become very clear that the Imp is like a barn door w/regard to mpg. Keep it slow, and you'll get amazing mpg. Drive fast (+10 mph over speed limit) and you will, literally, pay the price. I commute 40 miles, 10 miles of interstate, 5 miles city, the rest 55 mph two-lane with lots of stops. Driving 5 mph below the limit got me a whole tank at 37 mpg! Driving with traffic at +10 mph gets me 28 mpg.
Yes, to driving sytle and driving conditions. All city driving isn't the same. If you fire up a cold engine and drive it 2 miles, shut it down and then fire it up again 4 hours later and drive 5 miles, well, your MPG will SUCK even on the most efficient of vehicles.
Assuming a vehicle is mechanically sound there can be a massive difference due to driving 'style'. Check my 2011 Subaru Forester's MPG vs other 2011 Forester's MPG on this site. It will be a real eye-opener. If you drive 'smart' EPA ratings can be beaten and beaten by a lot. My car returns 27% OVER the EPA rating for the life of the car.
Being a new Ford Hybrid Fusion I am finding out so far the milage is off from the stated 47 by about 7-8 miles per hour. I maintain the speed limit in and out of city and best I've seen is 40.4. I only have 700 miles so far so I hope this number changes as time goes on. My dealer drove a C-Max for awhile and they both have the same motor and he said he did get 47. so we will see
My '07 VW Passat 3.6 wagon pretty much nails the EPA combined. Actual is 21.6 mpg and EPA is 22 mpg. I always have a roof rack on (windresistance and we drive closer to 70% city/suburbs with 0 commute miles. I drive aggressively but my wife doesn't. I can't complain. Anytime we are on the highway on long trips we have a huge roof top carrier and we are LOADED with weight. I have tried real conservative driving styles and can get the trip mpg to get to the high 20's occasionally. The stop lights is what kills my mileage in the suburbs. Anyway, not great MPG but its right at the EPA estimates for me.
Everybody drives differently so personal anecdotes here are meaningless (sorry...) The EPA estimates (rather what Subaru says are the EPA estimaes) for the CVT are inflated compared to Consumer reports and fuelly itself. Check the EPA highway mpg of all new cars that matched the CVT's 35 mpg highway. They get 30+/- 2 mpg on the EPA test. There are a dozen of them. That means the real EPA test highway mpg should be 30 as well.
Also on fuelly take the average of the manual transmission Imprezas vs. the CVT and you will see the manual transmission gets better mpg, even though it's EPA rating is less. 12's are the same as 13's.