I think it's not so much about the 'physical' part as about the 'rigorous training, certification and qa assurance practices' part. Developing software is very different from constructing a building (I do both, not as an engineer though); software is new, almost each and every time, because once it's build, you can just copy it byte by byte. Developing software is about pushing the edge in an unconstrained space. Physical construction (buildings, bridges, roads) is about repeatability; rigorous standards to reach a quantifiable production standard, and a build-in inertia to change. Large outfits (IBM, IT dev depts of big-four, that sort of thing) want to get software development to those levels, but nobody has managed so far.