I was thinking that you'd got some information about the machines Shapeways uses.
Shapeways uses three different sizes of printer for WSF, the production team decide which model is printed in which printer - obviously smaller models should be printed in the smaller maching, but this is not always the case. It may be that the smallest printer Shapeways used is reliably capable of sub 0.7mm dia wires/wall thickness, however to cover the bases Shapeways have chosen design critera that works for all of the WSF printers they use for the reasons mentioned earlier.
The first 10 minutes of the recent
Shapeways Live broadcast with Bart and Alan goes into some detail on the hows & whys, and at around 13:40 there's a bit more of an explanation about the whys of walls & wires. Alan also says "For particularly wirey models the minimums might not be quite enough."
Paul
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Last edited: Jan 23, 2013