> My suspicion is that this divergence could have to do with the ongoing existence of the US penny

The penny should be gone. Same for the dollar bill; coins last 30 years vs seven for cloth bills.

Yes, the penny should be gone.

But I disagree about the $1 note. According to the GAO, replacing the $1 note with a $1 coin would actually result in a net loss to the government:

https://www.gao.gov/assets/700/697778.pdf

Thanks for the info; I hadn't heard about the increased life of paper bills.