Cole,
These threads evolve and folks add to them at various points, sometimes with redundant information. You know this. Heck if we really want to pick on it the OP asked "I'm trying to find the best tablet... stand alone GPS navigation, photo review and basic editing, light internet surfing, etc... I've got a budget of $500 or less with accessories."
Your test is valid BTW. However your circumstance may not have needed the aGPS.
aGPS devices use available location references from WiFi and/or cellular networks to assist the GPS chipset in it's location duties (triangulation, almanac etc). This is particularly helpful in areas that have a heavy canopy like city centers. This capability can speed up initial position lock but that's not given in all cases. This functionality does not require subscriber information (ie Data Plan) to function, only that the cellular or Wifi radio's be active.