I think he, quite cleverly, submits these just before the week delay for subscribers expires to maximise the advertising for both Lwn's excellent content and their early-access subscription service.

It may be just as you say. But I still think that while it's ok for Corbet to share it widely, it's not ok for just any other one. That is why submitter on HN should add comment that the link was shared by Corbet on reddit in the first place.