Just because it's technically possible to do something from an engineering perspective, doesn't always mean that you should do it. For example, TomTom's integration with Google Maps for POIs (be they expert edited or user generated) allows users to update their P-Navs with the freshest content via a save to GPS option in Google maps. The data is then uploaded to the device via a desktop offline sync and then users are ready to go. Sounds like the iTunes-iPod paradigm to me, and well, I think most acknowledge that works just fine for music content. So why not maps?
A connected PND with access to the Internet doesn't make it any better than an offline one. In this particular argument, adding a chip to connect to the Internet means the user gets charged twice - once for the device and many many times more for the service - and that sucks. I'll take the offline iTunes-iPod paradigm, thanks.