Besides, the "South" that is becoming part of the "Democratic wave" is the Atlantic seaboard, including South Carolina, not all of the South. Clearly Landrieu was the only vulnerable incumbent Democrat and merely did ok while Obama did far worse than expected in every Southern state without a sizable black population. Look at Missouri or even Arkansas.
I'm also not sure how well Landrireu would have done if her last name was something like Landon. She probably still would have won, but there's a rule of Cajun voting that all else being equal you back the Cajun
I wouldn't really include Missouri as a Southern state; we are very Midwestern. And remember, Obama did better in Missouri than John Kerry did. Obama only lost the state by less than 4,000 votes due to a large turnout in the Republican strongholds of Greene County (Springfield - Roy Blunt's district) and St. Charles County (St. Louis exurbs) that offset his margins in the Democratic strongholds of St. Louis and Kansas City. He won Boone County (home of the University of Missouri-Columbia) and Jefferson County (St. Louis southern suburbs) that Kerry lost, and Obama even won two rural counties (Washington and Iron) in Southeast Missouri that Kerry was unable to do so I'd say Obama did pretty well in Missouri across all demographics.
As for Arkansas, it was the black sheep of the election. It was the state that swung the most Republican and I believe Arkansas has a larger African American population than Missouri. Obama did underperform in Arkansas, a very Democratic state, whether it was racism or disgruntled Hillary Clinton voters who crossed over and voted for McCain, I don't know. Arkansas is the most Democratic of any of the Southern states--both U.S. Senators, three out of its four House representatives, the governor and all statewide elected officials are Democrats, and Democrats control a supermajority status in both chambers of the Arkansas state legislature. Undoubtedly Hillary would have carried Arkansas so I'm sure the reason why Arkansas swung so Republican is because she wasn't the nominee. Call it a true, undying love for the Clintons in their home state or hidden, deep-seeded racism ..it's up to you.