Well, that actually belongs in the TV and HD-TV programming forum, this is more for DVD releases.
I can give answering this a shot though, I believe it is likely due to the fact that Fox has gone to a year-round programming schedule unvailing new shows in June, October, January and I think March. I'm not sure exactly what the thinking was on waiting until January to bring back 24 but it seems like it might have been done to help boost some of the newer shows that will debut around that same time.
that doesn't make sense to me at all. FOX hasn't really had any good shows on since X-Files. Every new show they premiere gets cancelled right away. They should just have the whole timeslot filled with reality shows, seems thats what people like these days which is beyond me, I hate that crap.
I think it also has to do with Fox wanting to air the episodes consecutively without preemptions. Since the Fox fall schedule typically does not get underway in earnest until after the World Series in November, it does not make much sense to play an episode in early September and then have the show disappear for 6-8 weeks and expect people to follow the storyline. Plus, this gives the creators more time to write and produce the season. ABC is doing the same thing with Alias this year. Season 4 will not begin airing until January, 2005.
Fox and other networks (notably NBC) are restructuring to year round schedules to compete with cable etc. While you (and I) may not care for whatever reality show they program, they are doing what they think will work to win the timeslot. Somethings will work, some won't and then it's back to the drawing board, or at least tweaking, but count on a trend towards HBO style staggering of shows in the near future.
Variety indicated in several articles that the reason 24 was pushed to the January season launch is because it's ratings had slipped a bit, and Fox wanted to use the fall launch period (which is in Nov. for them, due to baseball playoffs) to push what may be stronger material ratings-wise. They know it's a gamble, and one they may lose.