They are most likely printing things that 1) don't move, and 2) aren't subjected to any type of stress or heat.
I can't imagine that you can print something layer by layer with fused powder and expect to make anything as solid and tolerant as the normal (crystal) growth and/or casting/molding/etc processes make.
NASA is set to launch in 2017 a rocket stage that was in part '3D printed' via a form of laser sintering. [1]
Additionally, many aerospace parts (F22 air vents, for example) are produced in a similar fashion. There are a series of Google Tech Talks on the subject [2]. In short, complicated shapes can be produced with less waste (versus milling from a larger block of material), greater tolerances (no warpage from welding heat, curing of glue), less labor (no assembly jigs), and usually less mass (due to partial infilling of material cross section).
Lastly, you'd be surprised at the number of molds that are now being made via '3d printing' (I'm growing to hate this term) for composite applications. Normally they are CNC'd from aluminum (or 'tooling gel') - whereas smaller run items can be laser sintered. My startup uses PLA molds for vacuum infused carbon composites which we print from a RepRap Mendelmax. (router enclosures, antenna mounts, UAV and motosports stuff, etc).
They are most likely printing things that 1) don't move, and 2) aren't subjected to any type of stress or heat.
I can't imagine that you can print something layer by layer with fused powder and expect to make anything as solid and tolerant as the normal (crystal) growth and/or casting/molding/etc processes make.