For those of us that have been paying attention, it's been pretty clear for many years that hybrid vehicles can exhibit a great deal of variability depending on the driving conditions. Back in late 2010 when I was working at GM and they were launching the Volt, they spoke extensively of the 3 Ts and how they would affect the electric driving ranging. 

Those 3 Ts are terrain, temperature and technique. All vehicles get worse mileage in winter for a variety of reasons http://green.autoblog.com/2009/11/12/greenlings-why-does-mileage-drop-in-winter/ but hybrids are particularly sensitive because battery performance is reduced as the temperature drops (or gets too high for that matter).

As the boys from Top Gear demonstrated a few years back when they raced a Prius against an M3, driving aggressively in a hybrid will also degrade efficiency because the engines are  tuned to operate best under the light loads typical of the driving cycles used to estimate efficiency.

Nair talked about these factors as well as break-in effects when he spoke to media. He specifically mentioned a 5 mpg improvement as the vehicles go beyond 6,000 miles on the road. Since the C-MAX and Fusion haven't been on sale for very long yet, they will probably get better as time passes. A check of the user submitted numbers on fueleconomy.gov http://www.fueleconomy.gov/feg/Find.do?action=sbs&id=33010&id=33083 already shows the averages climbing from where they were just a couple of weeks ago.