In a 50/50 election, McCain would win more than by single digits. The reason Obama is polling well is because as of now, according to Rasmussen, the election is not 50/50. It favors Obama.
The national margin corresponding to this state poll was Obama +5, i.e., this poll says that SC is McCain by national margin + 14 points.
So, if Obama wins 50-48 nationally, he`d lose SC 55-43 ... Sounds about right.
BTW: They'll probably release the TX poll today, because they removed the announcement from the Daily Tracking story ...