Metal-based laser sintering (SLS) has been used in high-end research and industry labs for the better part of 10 years (or more!). It's just the democratization provided by outfits like ShapeWays that is making it available to the masses.

People already use the casting solution you suggest. I remember the early Autom (robot) prototype used silicone casts [1]. I'm sure there are many other examples too...

[1] http://www.hizook.com/blog/2009/11/22/building-robot-heads-u...