Treasuries and Treasurys ... Why the "Y"

Treasuries vs. Treasurys ... we get questions about this from time to time. The latest example was a missive to Jeff Cox, one of our more prolific staff writers.

Hello Mr. Cox:
Great article, but your spelling of "Treasurys" is incorrect. Shouldn't it be "Treasuries"?
Online Grammar Watchdog

Jeff's answer (and our standard policy) ...

Legitimate question. ... The short answer is that the "misspelling" is on purpose, done to differentiate Treasury bonds from the plural for the Department of Treasury, though I'm not sure why you'd ever need to pluralize that. In any event, a number of business news organizations, including CNBC, use the "Treasurys" spelling. Thanks for the question, and keep reading!

Just thought I'd print the exchange here in case anyone else also wondered.