It seems like a valid reason to me? I mean it is true anyone can try the game for two hours and then refund, so it is free.
But I think more important reason for no PC demo is because they do not want to make cracking of the final game easier, and demos can sometimes help crackers with the access to executable.
Admittedly this is anecdotal, as I've not yet had to refund a game - But I heard that if you refund two games in quick succession, Steam get the grump on and challenge the refund.
Again, this may be me being naive, but I can't imagine it'd take much to produce a demo that shuts off before the story gets real interesting...
It just smells of a bugged PC release, but we shall see...
Not entirely sure that I would agree with Mack that we havent had games that come close to Half Life for immersion, one of the most immersive games I have played ever is Alien Isolation, I suspect there is a little tinting of rose on his glasses maybe.
I was really surprised to hear Mack getting all gooey about a game that hasn't been released yet - That's never really been his style... You know that if it's a pile of garbage, he'll probably slate it worse than No Man's Sky though