In "The Lottery," what normal law of probability has been suspended in the story? Granting this initial implausibility, does the story proceed...

A fine question. Given the size of the town (as indicated in the story), I'd have to say that it is the fact that Old Man Warner hasn't been chosen.

At one point, we're told the following:

"Seventy-seventh year I been in the lottery," Old Man Warner said as he went through the crowd. "Seventy-seventh time."

Given the limited number of names called, he should have been stoned to death a long time ago.

Now, emotionally, the chance that seems least likely is Mrs. Hutchinson first forgetting, then getting chosen.