I think the question is probably backwards. If you don't like the lapse of time between announcement and release, the question should probably be, "Why does Samsung announce a new phone so far in advance of when it will be released?" I mean, the Note 2 was released in late October of 2012, and I think (but I'm not sure) that the Note 3 was released in October of 2013. One-year cycles probably make sense for a lot of reasons, including the two-year upgrade cycles that most U.S. carriers have, and it probably takes a full year to plan and design the software and hardware, get component manufacturers on board, build prototypes, test it, get carriers and retailers on board, ramp up production, and have sufficient stock on hand to be able to ship to retailers all over the world to sell millions within weeks of a release date. So the fact that the latest version, Note 4, is again being released about a year after the previous model makes sense to me. It's not like Samsung is sitting on millions of Note 4's and just wants to make us wait for six weeks after announcement, and it's also probably not that they could have accomplished all of this a few weeks earlier.
So, why did they announce on Sept. 3 when release isn't until Oct. 17? Probably to generate buzz, to let people have some time to learn all about the phone before making the decision to buy, and to convince some people not to buy the iPhone that is hitting the market sooner. I don't think it would have been a smart move for Samsung to wait to announce the Note 4 until after the iPhone 6+ was already on the shelves. Apple chose to wait to announce the new iPhones until closer to their release date, but if the Note 4 was going to be released on Sept. 15, perhaps Apple would have been wise to announce before then.
Bottom line, no matter when Samsung announced the Note 4 (for example, Sept. 3, Sept 30, or Oct. 15), you'd still have to wait til Oct. 17 before you can buy one. I'm OK with a one-year cycle between new models, so I'm OK with waiting til that late October release date rolls around. The fact that the announcement date was six weeks earlier doesn't bother me. Blockbuster movies sometimes show trailers many months before they are released in theaters.