Applebaum is right to argue that American and European activists are probably much more willing, because of their politics, to be moved by cases of genocide where putting an end to such violence does not directly benefit American security or economic interests.
I don't think that's right at all, and I think it displays a sort of paranoia about the American left that is more befitting of the far right than Applebaum and TNR.
First, obviously, there is the fact that what is going on Darfur is qualitatively worse than the activities in North Korea. This isn't to minimize them, only to say that while brutal concentration camps are bad, a systematic policy of ethnic extermination is worse. However, I think the big issue is one of perceived capabilities. When I was asked by some of my more liberal cohorts why I supported a war in Iraq but not North Korea (that's right, it was far more likely to be my liberal friends than my conservative ones who brought it up), I would invariably respond that "ought implies can," and while an intervention in Iraq (and Darfur) was very much plausible from a military perspective, an intervention in North Korea would be a full-scale war of the type we haven't fought since Vietnam. Now, it may well be that I underestimated the degree of "can" available in Iraq. But insofar as Darfur versus North Korea goes, I think the point still applies: liberal activists see a solution to Darfur that would not commit ourselves to the type of activity that the Iraq catastrophe has discredited, whereas in North Korea there seems to be precious little we can do to stop the concentration camps that would not imply unacceptable loss of life and treasure on our end.
Moreover, I think the descriptive argument about how Sudan is not a country we have "interests" in and is not tagged with any of the buzzwords (communism, radical Islam) that provoke controversy in the modern political sphere is wrong as well. We do have interests in Sudan, both in terms of oil wealth and because we have an interest in checking China's influence in the region. The existence of these interests may not be as widely known as comparable ones in Iran or North Korea, but it is just wrong to say that a Darfur intervention would not objectively aid the US or step on the toes of another great power. Furthermore, it is unclear why these issues would not be presented more frequently in the public eye as Darfur rose in prominence. A similar claim can be made as to the "buzzwords" argument: Sudan, after all, is a Muslim state, and has tried very hard to link Western or international intervention in Darfur with charges of anti-Islamic bias and neo-colonialism. Why haven't these allegations had more of an impact, given the left's continued ambivalence towards charges of imperialism and anti-Islamic sentiment?
I think, then, that the focus on Darfur is not a manifestation of relief that it does nothing for the West, but is rather rooted in an honest and genuine recognition of how uniquely appalling the activities there are, and a firm belief that the US and the world could be doing much more to stop them. Now, history will judge us based on whether we act on those beliefs, or simply lay them aside as we have so many times before.