Why the Nintendo 2DS Makes Sense: It's Not For Gamers | Will Greenwald | PCMag.com:

The 2DS is cheaper because it lacks that hinge and includes the ability to build the two "screens" on the 2DS with one LCD panel and a plastic bezel. The cost of manufacturing the 2DS with a single LCD panel and a single enclosure is certainly less than the cost of building a device with two LCDs (one with glasses-free 3D) and two enclosures connected by a hinge.

Kinda embarrassed I didn't immediately figure that out myself.  Clever girl.

Edit: I'm also surprised with all the press saying this is a highly targeted design for young kids to stick in their backpacks rather than their pockets, and won't have more universal appeal.  As if the iPad suffers for not having a "clamshell" design.  (The original iBook; that had a clamshell.  Anyhow...)  My DS usually sits on my desk.  What do I really care if it's essentially a tablet?

This, my friends, is a great example of a minimally viable product.  No 3D, no folding, no stereo speakers, just mono.  Who cares?  If I didn't already have access to a 3DS, A Link Between Worlds would probably have me shelling out for a 2DS this holiday season.