... the discovery raised questions about whether omega-3 fats really were protective for everyone, despite decades of health advice. “The same diet may have different effects on different people,” he said."
This is a very key point. We're just beginning to scratch the surface on how genetics and diet interact.
I blame it on our cultural ideals stating that everyone is equal. As Americans, we have severe reservations about claiming people are genetically different.
Differences in gut flora could be another factor.
Seriously though, this is a core part of dietary concerns, it's almost a certainty that a Russian is going to have a slightly different reaction to foods than a European, due to centuries of eating different foods. I think it's only recently we've really started to discover that evolution isn't just survival of the fittest, but a considerably more complex mechanism that has immediate impacts after very few generations to very slight stimuli. Not to mention stuff like gut flora, environment during pregnancy, etc.