Yes I find these sorts of comments as GP to be hopelessly naieve. It speaks to somebody who has never worked on a large project (think 4 teams of 10-20 developers spread across NYC, London, Tokyo, and Hong Kong) or a long-lived project (think 10 years).
That sort of minimial, incremental approach does not scale at all. Software engineering in the large requires, as you say, interfaces at every boundary and a near-religious understanding of how all the different components and boundaries fit together.
I agree, though from the other side your sort of comment does not acknowledge the fact that a lot of projects do not require that kinda of scale.
Fundamentally they are very different practice of software development and I think what OP talks about are those many cases where there is no scale need, never will be, yet we see this design approach that is suited for the type of projects you talk about.
That sort of minimial, incremental approach does not scale at all. Software engineering in the large requires, as you say, interfaces at every boundary and a near-religious understanding of how all the different components and boundaries fit together.