The Case of Pittsburgh’s Missing Comma

This email from Lori Randall appeared in my inbox the other day:

I’ve been enjoying your book How to Not Write Bad, but I came across a passage on page 19 that puzzles me. Here’s the passage in question:

 

“The majority of my students would write Pittsburgh, Pennsylvania is his hometown - leaving out the (required) comma after Pennsylvania because they wouldn’t pause at that point in the sentence.”

 

I can’t think of any context in which a comma would be required after the word Pennsylvania in ...