Specifically, why do I always see an icon for "Free Public Wifi" on my lap-top when I'm looking for a network?
Apparently, there was a bit of a bug (one of many...) in Windows XP in terms of how it handles certain situations, and it effectively created a "virus" in that unwitting travelers around the globe are all broadcasting "Free Public WiFi" from their computers without realizing it, after they tried to connect to such a network:
When a computer running an older version of XP can't find any of its "favorite" wireless networks, it will automatically create an ad hoc network with the same name as the last one it connected to -- in this case, "Free Public WiFi." Other computers within range of that new ad hoc network can see it, luring other users to connect. And who can resist the word "free?"
Not a lot of people, judging from the spread of Free Public WiFi. Computers with the XP bug that try to connect to the Internet will remember the name, create their own ad hoc networks and entice other users wherever they go.
And so it continues to spread. No one's quite sure where it started, but somewhere way back when, someone set up such an ad hoc network in an airport (perhaps as a joke or a honeypot), and it got picked up by others... and then it just continued spreading. Eventually, it should die out as Windows XP machines finally go extinct, but for now, enjoy (but don't bother connecting) the "Free Public WiFi" found in so many airports...
Its noted in the comments that XP service pack 3 fixed the problem, indeed I haven't seen the icon on my laptop for over a year.