[derefr]

But would it still cost more if the building were made of prefab-stamped “IKEA pieces”, rather than stick-built? I.e., if you had to build the house 100 times (for a townhouse development, say), and so “factored out” the assembly of the framing and drywall and etc. for each curve and corner, would the labor costs then approach equivalence?

[jtbayly]

No, because those joints still need to be created somewhere in the process. It might be cheaper than the one-off build, but it wouldn't be cheaper compared to a more efficient design "factored out."