Even in Japan, toy sale during the Holiday season spike, so introducing new stuff right before or during the season would mean good things for sales.
Rurmor's are that Sentai is gonna make the jump from running Feb-Feb to Sept-Sept for the same reason during or after the 35th anniversary series (the one after Goseiger).
That was my running theory, and I said as much in a previous thread:
Using your theory, 31 episodes makes no sense. 13 would. 26 would. They had almost no clue what to do after the would tour, leading me to believe they had chosen a specific ending date ahead of time (and thus a start date for Double), and then wrote the story to fill out what they had left.
Decade had a finite point at the end of the World Tour, and then they meandered a bit. My theory is they purposefully wanted to shift the start date for Kamen Rider for whatever reason. Catching the Christmas sales is an excellent reason that makes business sense.
Well, in all likelihood it'll result in better shows. Usually what tends to hurt Rider is that after the initial wave of toyetic debuts, new stuff would have to be rushed in so there'd be toys debuting in fall for Christmas sales.
If the initial wave of toys is hitting in time for big Christmas sales, then the rest of the series can be more leisurely about introducing new forms, power-ups, vehicles, and etc as the show builds toward an ending.
As we've all thought (and this is my theory), Decade will reare his head once again with W and the future Heisei Rider, and we'll have an all-Heisei Rider team-up once again next fall..........which will renew the old Showa Kamen Rider tradition of past and present Riders teaming up together to take down some badass enemy.
Then again, next fall will also be the 40th anniversary of the Kamen Rider franchise, so this was to be expected anyway