Answer 1

(from W3Consortium, https://www.w3.org/TR/2013/REC-geolocation-API-20131024/#coordinates_interface )
"The accuracy attribute denotes the accuracy level of the latitude and longitude coordinates. It is specified in meters and must be supported by all implementations. The value of the accuracy attribute must be a non-negative real number."
I guess it has to do with the possibility of the API to use the device's GPS (higher accuracy, lower value in meters, I presume), or not (just GSM signal, lower accuracy, higher value in meters)... But just my guess...