I think Norvig acknowledges the point you are making here, namely that the statistical approach does not explain the cognitive systems behind language. However (if I understand correctly) he implies that those systems might be too complex to be adequately explained, let alone emulated and we can achieve more by observing them as black boxes, analyzing their outputs, i.e. language as it is used.
"if a computer could - like humans - learn to produce infinite, novel, contextual, and meaningful grammatical utterances"
To perfectly achieve this goal, you might have to simulate 4 billion years of evolution under the same conditions as it happened on Earth, and a few thousand years of cultural evolution as it led to our languages and our cultural context. Language is incredibly complex and changing, many of its details might be incidental, i.e. results of random events, so it seems unreasonable to pretend that we can deduce it all from some elegant first principles. At least that is my reading of Norvig's argument.
"if a computer could - like humans - learn to produce infinite, novel, contextual, and meaningful grammatical utterances"
To perfectly achieve this goal, you might have to simulate 4 billion years of evolution under the same conditions as it happened on Earth, and a few thousand years of cultural evolution as it led to our languages and our cultural context. Language is incredibly complex and changing, many of its details might be incidental, i.e. results of random events, so it seems unreasonable to pretend that we can deduce it all from some elegant first principles. At least that is my reading of Norvig's argument.