This appears to be true on the surface but is not accurate. I am a structural engineer and when people need to do something with their buildings, the engineers (structural, mechanical, fire, etc.) and the architects need the plans or at least a survey. If a side has the plans and the authority on the plans, that side has huge leverage over the building. Fortunately, this is never the case with buildings. Plans are considered public information. It would be so much better if the same applied to software.