Yeah the posts in this thread seem to explain it, and before this becomes a "strategy to beat Opelucid Gym" thread, I'm gunna lock this. Also mainly because there's threads on the hardest gym leaders and such, and while I'm usually open minded with theory threads like this, this one just seems to become a little too specific and with the evidence given there isn't that much to back it up. However you're free to make a thread on why you think the Winter season has increased changes in the games more than the other seasons if you want, but otherwise there isn't really that much to discuss other than how to defeat the gym. But yeah, just spend time around Dragonspiral Tower and Cold Storage and you'll see there's no favouritism towards Winter in terms of the Pokemon that can be obtained.
Feel free to get involved in discussions in B/W's other threads though! :)