Only a flatworm would not have predicted the Cadillac ATS would help increase sales for America's erstwhile luxury brand of record; however, even the best automotive oracles didn't realize by how much: The ATS fueled a 49-percent increase of the brand's year-on-year sales in March, the sixth straight month of growth for Cadillac. The momentum helped push General Motors to post a 6.4-increase in sales in March versus 2012, leading its domestic competitors.

Dealership salesmen are among the first to register the shift occurring at Cadillac. A Texas dealer related an incident in which he helped a mother affix a baby seat in a car for a test drive, explaining that as opposed to the older buyers that are still a Cadillac mainstay he's getting "a pretty diverse group that's coming through the door now" who are "younger and better educated." Aided by incentives on the ATS, Cadillac's sales are up 38 percent so far this year, overtaking Acura as the fourth best selling luxury brand, and GM stock is benefiting with incremental gains because of it. Based on early response, the new 2014 Cadillac CTS should keep things going in the same direction.

The trend at the Wreath and Crest is part of a larger sales trend happening among domestics – with other models like the Dodge Dart and Ford Fusion doing well – and overall US car sales. Head over to Bloomberg for the big picture and role the ATS plays in it.