This is a fault with most ISP?s, and that there is no static IPv6 address for the account. There are enough IPv6 addresses to give every person in the world 1,000+ IP addresses, before one has to worry. With that said, it would just make sense to have a static IPv6 IP address. This is not a fault with just Comcast, but every ISP I know of does not provide a static IP address to their home customers.
So what can Comcast do? Well, simply put – provide a static IP address to their customers. As mentioned, there are well more than 1 address for every person in the world, and having a single IP address just makes sense. I don’t see this happening, but it would be nice.