That is a good point, but I guess you have to ask if you are willing to allow GPS to eat up the 22 or 23GB of high speed data (of course we have no idea what kind of bandwidth the app uses) or would you rather take a chance on downloaded maps.
I do remember your blog post on CoPilot and pretty much agreed with your conclusions. I have actually used CoPilot with a separate Bluetooth GPS receiver and a Windows phone way back when. That was way before the mobile phone world had matured to its current state... and even now, there is a long way to go.