The European tests are also flawed, they might be more realistic but the "mileage" is still not applicable to real world situations. The tests are highly optimized, there is almost no way to get these results as an ordinary driver.
There as a consumer program on TV a couple of weeks ago, people were complaining they were only getting 16km/l instead of the advertised 25 km/l for a certain car. This was after driving instructions/coaching from the importer. The conclusion was something like:
Every car is tested in the same way, highly optimized. You will not get these results in real life, but you can use the results to compare cars, a 25 km/l car will be more efficient than a 20 km/l car of the same fuel type for the same driver.
BTW I am able to almost reach the manufactures mileage in my car, but it means I have to drive really slow, stay of the throttle (0-100 km/h in 20s), look ahead/anticipate to avoid breaking/acceleration, drive under the max speed limit, don't drive in the city, don't drive during rush hours, make sure the car is empty (not carrying unnecessary weight). But realistically this will almost never happens.