Sometime within the last year or so, the EPA revised all of the estimates for all cars. But they haven't yet made those numbers available to others in a developer-friendly format. When we set up Fuelly, we used the numbers that the EPA makes available here. The numbers you see on the site are from those downloads, and they are the numbers that are in those downloads today.
Until we can get those new numbers as a database, we're stuck. If we update them by hand, we'll spend months of development time looking up the correct numbers on the EPA website and changing them by hand and we just don't have the manpower.