simply hadn't noticed that Simpson's paradox was in effect
You don't understand academic culture. Steve Landsburg (like myself) is a college professor. Because of political correctness almost no college professor would dare point out what Landsburg just did.
You're underestimating both how good economists are at math and how bad we are at resisting political correctness.
ETA: The table linked by Landsburg has been called into serious question by Evan Soltas [H.T. CronoDAS]. I edited the post to leave only the table to provide context for the comment discussion of its status.
Economist Steve Landsburg has a post [H.T. David Henderson] about the supposed stagnation of median wages in the United States in recent decades. In the linked table median wages have risen for: