If you have the WiFi-only iPad your location is determined by nearby WiFi router locations. This is done by using a location database which contains the MAC addresses of routers and their physical location. A MAC address is a unique number which is built-in to all network devices when manufactured. The database is built and updated by other GPS-enabled devices actually seeing your router and then adding/updating the router location in the database.
Bottom line: your Wanadoo router is in the Apple location database but your new Netgear router hasn't been seen yet and added to the database. Ther isn't any problem with your Netgear router or your iPad.