The sentiment here is that it’s somehow unfair to developers to treat software labeled “beta” with the same critical eye as non-beta software. That’s true, in the case of actual beta software, where by “actual beta” I mean “not yet released, but close”.
Released vs. not-released is the distinction that warrants critical restraint. Film critics don’t write reviews of rough cuts. Book critics don’t review non-final manuscripts of novels.
Released software that is labeled “beta” is still released software, and is fair game for the same level of criticism as any released software. You can’t “semi-release” your 1.0 just because you want it out there but aren’t yet finished. Being semi-released is like being semi-pregnant.
Much as I have, Gruber makes some allowances for software which is freeware or open source and notes, appropriately I think, "That’s not to say such software is off limits for criticism; only that such software, when criticized, deserves at least some degree of slack."