Yes? Because we tend to stress ourselves up and panic, like I said. To accurately measure IQ we'd all need to have equal interest in the test itself, which we don't. THIS is the main reason why the results differs so much between individuals and NOT because we're necessarily smarter than the other. SoooOOOooo, what is the interest we all share in common that could be combined with an IQ test? Well, it's surviving, most of us wants to survive right? And again, IF we'd somehow manage to take the stress out of the question this would be the most accurate way to measure our IQ; a gun pointed at our heads as we solve it. At this moment our senses would work at their full potential, equally, and we would not only get very high and accurate results, but they would also be shockingly similar to eachother.
Something similar was tried in the USSR military: people scored very differently before the education when solving puzzles; they scored even more differently during the start of the education as intense pressure was combined with puzzlesolving (due to stress and panic of course); but they scored almost identically towards the end of the education as they were trained to handle pressure better, only the few that could not yet handle the pressure fell short. It was evaluated that when they started to share equal interest for the tests with time, their results got close to identical as well ..and much better than their results prior to the education.