Actually Blue, based on the article at Covers.com, it's because of SD's QB rotation. Apparently Brees and Rivers are fighting it out and will see more time than most expected. It's been about a 6 point line swing since the spread was put out last week.
Tomlinson and Gates and Edwards all are OUT, not that it matters all that much anyway. But i prefer the +3 1/2, buying half a point for GB at Lambeau over anything here..