There just don't appear to be any factors--at all--which would suggest North Dakota as more favorable to Obama than South Dakota in terms of demographics or voting patterns unless a Canadian infiltration of North Dakota is the prelude to invasion.
That's not true. SD has the rapidly growing Sioux Falls area, that while more liberal than most of the state and ND, also has far more partisan Republicans who'll never change their vote. And it also has Rapid City, which is even moreso partisan. ND doesn't have any equivalent the size of Rapid City, nor does it have anywhere comparable to suburban Sioux Falls (suburban Fargo isn't as big.)
I also strongly dispute that SD is slightly more favorable for that reason. All the 2004 results show is that the floor for the Democrats in SD is higher than it is in ND. And even then Kerry no doubt over-performed due to SD's anti-incumbent streak. Probably not much of a difference (compare Bush's numbers in both state in 2000.)