Keep in mind what is sent is not just your wifi spot, but every one the device can see. And the Apple servers simply use this info to initially seed the search, and in turn, the servers then send back all the wifi spots over a large area near you. From my understanding, the device never transmits the signal strength, and all the actual precise triangulation is performed on the device. If you are in Maps searching for directions, it also sends down the spots along the route, allowing for some navigation assistance while in route.

This info is being sent over the Internet much more frequently now, after the location gate cache scandal changed the retention of this data to be limited to one week on the device. It's unfortunate too, as I have noticed the reduced speed in acquiring my location after this change was made.

I also don't really understand the privacy concern here. For Apple devices, every user must opt into location services. On any iOS 5 device (upgraded or new) disclaimer is readable right from the initial spot where prompted to turn it on. How much more prominence does this info need? And do you have similar privacy concerns when your device requests map data around it, possibility revealing that you are looking for directions in an area?