What's interesting, but kind of glossed over in the article, is it's not just your typical plastic 3D printer. This thing prints metal objects, which could conceivably be used for car parts.
A quick look through the materials catalog at Shapeways[1] will give an idea of some of the available technologies and things that are possible, and that still doesn't touch on what's going on with the more industrial-scale technologies as referenced in the article.
[1] http://www.extremetech.com/extreme/175562-major-patent-expir...
The advantage of 3D printing comes with making very complex shapes. As far as I know, most parts in a car are pretty straightforward (gears, shafts, pistons etc.). Am I off-base?
The problem with metal fabrication is that a good CNC machine is at least $50,000 and more normally $250,000 or so. Combine the fact that the shop owner wants that machine running 24/7 to make bank, the fact that an error in the steel can cost you $20,000 in raw materials, and the fact that a single programming bug can damage the machine and you have a recipe for very constrained, conservative usage.
Contrast this to 3D printers: "Huh. That sucked. I'll print it again." Material lost: Under $1000. Machine damage: Nil. So, you'll print all manner of crap until you get it right.
A good example of part-strength is the 1911 Solid Concepts in Austin printed late last year[0]. They used a EOSINT M 270, a pretty advanced and expensive SLS printer. [1]
For reference, that 1911 ran about $600k in build cost. yeesh.
[0] - http://www.thetruthaboutguns.com/2013/12/robert-farago/gun-r... [1] - http://gpiprototype.com/services/eosintm270.html
First, metal is a LOT heavier to throw around than plastic. So, your control systems have to be dramatically bigger.
Second, the melting points of metals are way higher than plastic, so the energy required to be right at a critical point of flow/melt is a lot bigger. Not to mention the percentage difference between melted and not melted is a lot smaller.
Third, a lot of the metal techniques are about melting metal in place. That means that the part is buried in a block of powdered metal. That block of powdered metal is a significant fraction of the weight and cost of a plain old hunk of whatever the metal is. Try imagining fabricating even a small gold part out of a powdered block of 6"x6"x6" of gold--now think about how many metals are WAY more expensive than that.
Finally, powdered metal is explosive. Most machines working with powdered metal require nitrogen atmosphere pump down and if there is a leak ... KABOOM.