Don't most (mobile) devices broadcast all known SSIDs just in case a network is available and hidden? I don't really know a lot about the subject matter, but as I recall this does not apply to just iPhones.
I also remember an installation at the Datenspuren in Dresden with a monitor showing all of these SSIDs it intercepted with people walking past and being astounded how the device knew their home network name^^
Almost all Android devices do the same, they just send probe requests with all known networks. That is why you can automatically connect to "hidden" networks. Just run kismet or wireshark and see for yourself.
I also remember an installation at the Datenspuren in Dresden with a monitor showing all of these SSIDs it intercepted with people walking past and being astounded how the device knew their home network name^^