said by andyross:ALL D3 modems are supposed to support IPv6. It's this testing to verify that it actually works properly. It's the same with routers. Just because they say they support it doesn't always means it works.
+1. The reality is that it is easy to declare that IPv6 works on a spec sheet, especially when v6 was not really actively used by anyone. Now the real test is can it work for real in a production network and match v4 performance, etc.? The simple reality with any software is that if it is not heavily used it will either atrophy or be less mature since fewer people bang away at it in testing, use it it production, find bugs that get resolved and improve quality, etc.