You're right - it's going to be very difficult to get high tolerance parts using any method of 3D Printing. Don't say never - but isn't not as close of the koolaid machine would have you believe.
The result is definitely not crystalline, in fact it is better compared with regular sintered materials.
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.
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).
[1] http://www.engadget.com/2012/11/09/nasa-building-space-launc...
Usually they are simply cast and then reworked, which produces a blade of lesser quality than the single crystal ones but they are still quite usable (and a lot cheaper!).