As I understand it CC'ing lkml is accepted practice because it means kernel
developers get a heads-up/chance to review if a feature for a sub-system
touches other non sub-system code.
lkml can seem like a fire hose of information but I don't know how many
people actually read all of it and how many rely on filtering it for
interesting topics. Although I subscribe to lkml I only really follow
threads I've marked as interesting and/or involved with. To keep upto date
with the kernel in general I rely on the more usefully condensed information
on our very own LWN Kernel pages and more recently the very useful Kernel
Summary Podcast.