This isn't even an implicit thing going on within the buyer's head. Large companies do this explicitedly. The company I am right has people who spend all day l

This isn't even an implicit thing going on within the buyer's head. Large companies do this explicitedly. The company I am right has people who spend all day looking at "risk-reduction" in the engineering effort. They map the process and anywhere there is a question mark, they bundles of money to turn it into a check mark, especially if it is on the critical path. As an engineer you definitely don't introduce question marks for silly reasons like "lower billable hour rate", you would get chewed out for even thinking about that.