US did make a major commitment - especially since last August. Obama early in his term sent Scott Gration as a special envoy. In addition, Senator Kerry went in April 2009 and was able to get the triparty talks on this re-established and to get some increase in the amount of humanitarian aid allowed into Darfur. (When Kerry returned and spoke of the results, NPR asked a weird question of whether Obama sent him - rather than someone officially in the Obama administration, because of the likelihood that it could fail and that this distanced the administration - Kerry laughed and batted the question away. But, your point goes to this as well - Kerry has been the unofficial high level Obama representative here and in that trip and the later fall ones, Obama did have the luxury of it not being his administration.
This fall, Kerry was there twice - the second time with Obama proposals to get around some of the road blocks. Kerry has also been there since Tuesday. (If you are interested, I put a lot of last week's articles in this thread over in the John Kerry group -
http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=273x168182 I had been putting them in a GDP thread as well, but stopped due to no interest (esp after Saturday) Here's a video from today with Kerry and George Clooney!
Even if this referendum succeeds, which looks highly likely, there will be a period where they need to work out the separation and in addition, as Kerry makes clear, there is still the issue in the North of Darfur.
In addition to Kerry, President Carter with Koffi Annan has been in Sudan and his center was among many who were monitoring the voting.