I would bet that there is some factory work done to make the faces and threads clean and properly aligned, but that some frames could do with a second going-over.
I also bet that any factory assembled Surly (or any factory assembled bike) has similar factory facing and chasing done and is then assembled as-is, and this is usually sufficient.
This reminds me of the 'Are Raleighs Still Quality' thread from a few weeks ago - since Surly frames are made in a modern facility is Asia (Taiwan?), you can probably assemble without worrying about facing and chasing the surfaces and not have a problem, but a 1970s European-made bike would likely not function very well without pre-assembly facing and chasing of threads and headset surfaces.