ICMP weirdness

why not that seems ok to me.. ?

assuming you accept the 1918 assignment to your cable then its not unreasonable
that you can get to other end users on that network

Across other non-private IP space? I am not all that familiar w/
RFC1918, but I would think that this goes against it, or should I assume
that Insight Broadband is part of Comcast?

-Jim P.

Comcast uses parts of 10/8 for cable modem addressing, and these are
pingable from within the comcast network. Could this be some other
internal equipment address as well?