As a person who has spent weeks of my life trying to persuade AppCache + HTTP caches to do what I want (and who subsequently became a champion for the low-level primitives that became SW), I just don't agree with this.

It seems true in principle, until you try to actually get precisely the semantics you want, and then things go downhill fast. People should definitely try to find ways to use the HTTP cache more aggressively, but in practice, it's a giant slog with very little cross-browser consistency and total failures on mobile devices.