This is the answer. Gruber has and will continue to criticize Apple, but there has generally been very little room for daylight between his values and those of the company (either as expressed in their products or by their leadership). Also, while he doesn't say it, but I suspect that there has long been a feedback loop where his articles defending the company line are well-received internally and have helped him get press access to executives (for his WWDC live show) and preview hardware.
All that said, there has been a marked change since John's "Something Is Rotten in the State of Cupertino". Reading between the lines, it's pretty clear that Apple leadership did not like this article and snubbed him for his liveshow. Since then, there have been many more articles critical of Apple on daringfireball.net.