Hmm, I am not aware of Comcast (or any other large MSO) doing any NAT on large scale. Having said that almost all of the DSL customers in the US are being NAT'ed, but on the edge device (DSL modem) rather than in the core.
-- Scott Helms Vice President of Technology ISP Alliance, Inc. DBA ZCorum
How many instances of 10/8 did they say they were running? I was behind a NAT when I had Comcast service. I am behind a NAT currently with my AT&T service. Note that the NAT was done on the "cable modem" in both cases and not further in to their network. That said, from my reading of some industry large scale NAT devices (the A10 AX series is one which I am familiar with), they do things such as full cone NAT so it will still work with many applications that might break with conventional overload dynamic NAT.