Agreed. To me the pistachio that can't be opened is equivalent to the clam that doesn't open in the pot. Now you won't get sick from the pistachio, but the quality is never the same.
That's an old wives' tale. The clams, mussels, etc that are most resistant to opening are the ones that were in the best health, and thus the safest ones to eat.
Source?
Just google [unopened clams safe]. It's all over the Internet.