I was not prepared to be impressed with the Shapeways body. I am impressed. If this is the infancy of printed models, there may be a real future. Not sure the price point has been met yet, but still - impressive.
As this technology matures and the price comes down, I suspect you'll see it become the norm for small independent product producers. Laser cutters have already come down below $10,000 for units large enough to produce parts up to 24" wide.
3D printing is indeed in its infancy, but is now capable of producing parts usable for everyday static scale modeling. You should see the smaller parts we're getting from Shapeways in their most detailed process. The quality is close to that of injection moulding in some cases. The O scale Silverliner body is too large for the most detailed process and the finish is a little rough, but it's usable.
As to the price, 3D printing isn't for mass production just yet. It's for one-off parts and projects, or very short-run parts. The cost of the process will come down and the process will get better especially for larger parts in a few years, but you're still getting what amounts to 'custom' work, and the prices will be commensurate with that. I don't see an O scale MU body being that much cheaper in the coming years if only one or two bodies are being custom-made by this process. So, at least for the forseeable future, be prepared to pay a little money for the niche-stuff you want to see.
The best part is that the parts are easier to produce since no time-consuming and imprecise hand-work is involved and CAD can help get details even and consistent that you can't get by hand. That kind of quality is worth any price, and IHP is nothing if we're not known for a quality product. Maybe 3D printing still needs to catch up with our quality!