A GPS without a cell phone is quite capable of determining the correct local time and time zone if it has access to the current location and a map of time zones.
A Garmin GPS will always show the correct local time, and it doesn't have a cellular radio. Granted, cellular information can be used to assist less capable GPS systems used in some phones. But if a device is able to determine its location, then it is relatively straightforward to look up the correct time zone. Especially if the device has Internet access.
There is no technical reason why the Nexus 10 could not update the time zone based on its location information. It could be wrong occasionally (if the location is detected incorrectly), but IMHO that is better than requiring the user to manually change.