Games are art. Art's value is indeed subjective, being assessed by the viewer, but you can't objectively qualify subjective measurements, IE a more popular piece of artwork is not more objectively valuable than a less popular piece, because these assessments are subjective to begin with. So saying that the value of a game can be measured by its reception is like saying that classical music is no longer as valuable as it once was, because people love the shit out of pop music now. It's a bogus argument.
But more directly, The assertion that Tarn Adams consider's business immoral is utterly baseless. He made a decision, and that decision was that he would rather have complete creative control over his life's work than make a lot of money with it. For as Randian as this Sean Malstrom obviously is, it's awkward that he hasn't figured that out. And I don't think Toady was necessarily accusing Notch of selling out, so much as he's saying that Minecraft is pretty featureless. Which it is. It's a giant sandbox with randomly generated and completely disconnected content. It has no sense of purpose or direction, in design or in play. It's kind of a cop-out of a game. I find it fun, personally, but I totally understand the criticism.
Near as I can figure, this guy is essentially just angry because Mr. Adams is giving out his game for free. He makes no mention of any the failings of Dwarf Fortress, other than to state that it has graphics from 1978 (which is apparently a failing because it will 'never be mainstream;' IE, it will never succeed at a goal that it never had), and completely fails to illustrate why he might believe that Tarn should start charging money for DF, other than a passing reference to the 'ethical goodness of creating consumers.'
This guy isn't issuing a critique of Toady, Bay12, or even Dwarf Fortress. It's just a man on a ship passing at night, yelling needlessly at the far away lights on the shore.