firstly, get a better email client. Your existing one is broken.
Irrelevant, unhelpful and quite rude.
mailing lists are setup to retain thread sanity, its expected people use mailclients that can honour that. If yours cant and you prefer not to change it- perhaps consider using the centos.org forums instead ?
FWIW, on kmail on Fedora 14, at least, his messages show up properly threaded, even though the In-Reply-To and References headers are missing from his message. Don't know why Thunderbird doesn't show them threaded.
Of course, kmail has its own problems, particularly with putting in to many References headers on occasion, but that's a different issue.....
Some clients also thread by subject by default, I usually use claws mail for ML stuff as it's threading is excellent.
Says the guy sending this email in Outhouse....
Josh