Are you confusing having the ability to download map data vs having a GPS receiver?
The GPS will only provide your lat/long position. It shouldn't need WiFi or Cell access for that.
But if you try to display something like a google map, then you will need internet access of some sort (via WiFi or cell signal) to be able to download the map data itself.
However, if you purchase map data such as the Bizer or Navionics app, then you will have the map already on your system, and you won't need WiFi or a cell signal to use it. In this case the GPS provides your current position, direction of travel, speed, etc.
So unless I'm wrong, an external GPS device will only be an extra cost item that you may not need. Of course, I don't own an i-anything, so I could be wrong, but if they force you to have a WiFi or Cell signal to use the GPS, I just found another reason not to like an I-anything.
