The test-ipv6.com test will give you 7/10 if you are using 6to4 simply because 6to4 is less efficient than a native IPv6 implementation. The Comcast test does not make that distinction (possibly because they don't want to admit that their native dual stack implementation is not as widespread as they would like everyone to believe).
Here are samples of the two different (but somewhat similar looking) tests:
yea i ran comcast and now got 10/10. i just dont understand whats going on with the cisco cmts' there behind on ipv6 due to some codes or something. really sucks
Yes it sucks, and so does waiting for them to get operational IPv6 firmware for the business class SMCD3G-CCR gateway, but I prefer to wait instead of having them just pretend that it works and totally screw up my connection (like what happened with their first attempt at IPv6 firmware for the SMCD3G-CCR gateway a couple of months ago). -- We can never have enough of nature. We need to witness our own limits transgressed, and some life pasturing freely where we never wander.
If you are using 6 to 4 Tunnel it is because IPV6 hasn't been fully rolled out in your area and also you must be on a supported Router is you are using one. mydeviceinfo.comcast.com (Blue Banner) -- - Bill