Look at them there flame wars... Its like that footage from the Gulf War with all the tracer fire trying to shoot down the stealth fighters, lol...
Car and Driver uses the same VBOX testing equipment that many other magazines use. The VBOX is a GPS-based unit that measures acceleration times, top speed, track times, etc... all by triangulating positions with GPS satelites for the most accurate measurements possible.
Back in the day, they used to strap wheels with clocks on the side of the car and just hit the gas... The VBOX is much more accurate, and is considered to be the standard in the industry when it comes to performance figures.
Poverty, you mention that the European press often gets slower numbers than their European counterparts, and there are many explanations for that.
1) They may not have much expirience with the particular car or truck when compared to that of US Edditors. Car and Driver and Motor Trend Magazines both test numerous variations of different Corvettes, 3-Series', Evolutions, Mustangs, Ferraris, etc... every year and they have perfected what way to launch the car at a particular RPM and how to feather the throttle while doing so.
2) American test conditions may be varied greatly when compared to European standards. Humidity, temperature, elevation, wind speed, and even air quality can all make a difference when testing cars and trucks. Car and Driver and Automobile often test their cars in and out of the state of Michigan, Ohio, Indianna, and Illinois. Motor Trend on the other hand often does their testing in California, along with Road and Track. The Michigan and California are two VERY different places, and could account for some of the differences.
3) Conversions are another problem. As stated before, 100kph is roughtly equal to 62mph, so those numbers are automatically off. Horsepower numbers are also different in Europe and America as the gasoline/petrol is very different, with European petrol being much cleaner and lets the engine produce more horsepower.
My biggest bet is that the testers in Europe have no clue how to drive the damn things... Car and Driver has been testing the Corvette for more than 50 years now, and in just the past year the car made roughly 10 appearances, and they were everything from the standard Coupe, Convertable, Z51, Lingenfelter 402 Coupe, and Z06 (twice)... It helps to know how to drive a car now, doesnt it?