: Woah... that's GOT to be a coincidence. No way could that be organized...
: Halo 3 comes out on September 25.
Well, it is standard practice to release games and DVDs on Tuesdays. Season 3 of Stargate Atlantis comes out September 18, but you could probably find several titles coming out the same day with some similarly tangential connection to Bungie.
(Plus there's the fact Halo isn't Marathon.)
On the other hand, that's exactly the kind of weird coincidence that this site is built on. Well observed.