The unusual thing about comcast is they are an insanely large triple play provider with a heavy reliance on IP. Their triple play services ended up using about 8-9 IP addresses per household* . Of these only one (the customer's internet device) needed to be a public IP but comcast's system was so damn large and IP hungry that they ran out of space in net10 and had to start using public IPv4 addresses for internal management.
So while most non-botique access providers were probablly thinking "meh, when the IPv4 crises hits we can keep going almost indefinitely with CGN, lets let someone else be the early adopter of IPv6" comcast didn't have that buffer. They faced a stark choice between stopping expansion of services, federating their network**, or adopting IPv6. They chose IPv6.
That is why comcast is so ahead of the game on IPv6.
** That is splitting it into multiple sections to allow IP reuse and redesigning their management systems to cope with it.