I'm not sure, as I am not an attorney. The basis would be that without Hacker News website, there would be no Hacker News Monthly. It doesn't take a rocket science to imagine that running busy site like HN takes someones time AND money. HNM editor clearly profits off of it, just leaving all the costs to HN and squeezing essence out of it, making reasonable bucks for himself (again: kudos to the author; had I had time and balls to pull this of.... I'm just pointing out what would stop me from putting my time/effort into it)

I guess time will show (if HNM will keep traction) if HN will somehow, anyhow react.