@jscott69
You are right that Bonjour (zeroconf) is limited to the subnet you are on. The issue is that because it constantly broadcasts its own availability, and because a user isn't told if they left it enabled the last time they were on the Mac (PC), it can open a door to the system at any Starbucks, McDonald's, Denny's, or Public Library where you happen to be using your laptop.
That's probably not much of an issue for NSA (where equipment typically won't leave the campus) but travel a few miles South from Ft. Meade to Goddard Space Flight Center and you get a new agency acronym - NASA. I can assure you having supported Macs and PCs on 2 different NASA campuses as well as the Apple Store closest to GSFC, those employees do take their laptops home and use them on all kids of networks. This is to say nothing of the rest of the Federal Alphabet Soup around here. FBI, NIH, NIMH, CIA, USPS (ok, privatized but still ...), USAF, USN, USCG, USMC, USA, USSS, etc...
Zeroconf is also available to Windows and Linux users also.