I would still insist to have a country filter as the same model, same brand, same car can still have different specs in different country....the environment like weather and all affects as well how certain engine performs so in some country the fuel efficiency can differs significantly and thus looking at the whole world pool of users of the same car makes completely no sense at all...
Sorry about this, but we don't feel like Fuelly is big enough in other countries that a country filter would be useful. Looking at our membership we see that over 70% of users are in the United States. If you look at any particular model, there might be a handful of members from other countries, but it's not a significant number.
If you look at a particular model year, you can see the country flags listed on each vehicle. It's pretty easy to scan the list and get a sense of which vehicles are from a different country.
I hear you on different driving conditions, but the US itself is filled with dozens of types of terrain and climate—sometimes even within states. I don't think we're going to be able to meaningfully sort by geography to isolate differences in condition.