Yes it does scan surrounding wifi SSID because Google Maps uses Skyhook ( http://www.skyhookwireless.com/ , belongs to Google) to geolocate users faster than just using pure GPS signal. So does Apple which also use Google Maps geolocation services on their iPhones.
My guess is that Apple is gathering all those data in order to build their own Skyhook. It makes sense, specially when you keep in mind that Apple bough the mapping company Poly9.