No different from Cars. Its all about Sales too. Sales would drop significantly if the newer bows werent introduced during season when hunting is hot on everyones minds.
Not all companies have leaks before their dates either.

My Hoyt dealer is going to be one of the first to receive the 09 lineup, he figures within 2-3 weeks...by end of month basically. They still havent even revealed to him the NAME of the new bows....much less pics or specs. The ONLY thing he knows, is that they will no longer be DL specific cams this year. So it is still possible to keep a tight lip about the new lineup until you release it.
I think it is smart to release a new lineup DURING deer season, diehards will buy new bows regardless of release date, but the average joe schmoe is much more likely to buy the latest/greatest during deer season when he is into it big time. Mid to late October seems to be the same for the past2 or3 years now...thats about as far back as my release date knowledge goes..before then I didnt follow the new lines.