Well, what is the purpose?
If you take a look to Other Users, at any point in time there will be at least a few people that show up, but who aren't actually present, they just left Fullpage Chat or some other chatterbox client open. Such an automatic check of messages, either personal or chatter, should not register as presence, IMHO.
I don't plan on adding even more cruft to better support a scenario that's only temporary…
I can have no argument whatsoever with that.
It is not fair that a shortcoming in the site should be patched in a chat client, in every chat client. It is the responsibility of the site to treat these things properly, whatever anybody deems proper.
IIRC cookie processing, and thus marking the presence of a user, happens at a very early stage, before any custom node code can have a say in it. That way, a patch would have to dig very deeply into the guts of the site. I have serious doubts whether the people responsible for the state of the site would be so happy to have that happen.