My (amateur) understanding is that it is illegal. You raise reasonable points about the ethical question of informing the buying public about available products, but I think that legitimate journalistic purpose has limits. Exposing the internals, to the point of revealing construction and identifiable components, goes beyond that limit, as does holding the device hostage to confirmation. And I share the view of many other HN readers in feeling it was unecessary to make a public spectacle of the engineer who misplaced the device.
There are definite prohibitions on exploiting such information for commercial gain, even the indirect gain of internet traffic. Consider the benefit to manufacturers of knockoffs from such a detailed teardown - that undermines Apple's future sales and imposes an extra burden on US customs officials charged with enforcing prohibitions on fake devices entering the domestic market.