> a founder's ex-spouse (who had no direct participation in the startup)
Since both you and another comment so quickly zero in on the divorce aspect in this story, it's worth pointing out that Barbara Mikkelson was, in fact, a proper co-founder when snopes.com started, and worked alongside her husband for 20 years.
This situation is no different than any other founder leaving the company and selling his stakes. HN will have to find another way to blame this on women.
And, yes, there are mechanisms to prevent such problems. First among them would be the right-of-last-refusal: Before you sell, you have to offer the stock to the other co-founder(s), at the exact same terms you're offered. But that's not automatic, and has to be established early on.