Q4 is always an important time for retail but I don't think that this winter is that critical for Blu-ray per se. A case can be made that each of the last 3 winters were more critical.
If I had to name something that happened this year as being critical, I would point to the successful DTV transition. Consumers are now really getting into HDTV, with all indicators being that people want large 50+ inch 1080P sets. Since Blu-ray is pretty much gated to HDTV penetration, this is a very welcome sign.
Right now, look at the sales data since 2006, copiously posted in this thread. Look at the consistent trends that they show. Now look at player pricing (falling faster than anyone thought) and Blu-ray product that we are looking at in the next 3 months. The table is set.
Except for some external event in the world, I do not see anything that can happen to stop Blu-ray's continued progress. Q4 this year will simply mirror the last 3 years. By February, we will see a major influx of mainstream adoption.
At the same time, we won't see Blu-ray sales suddenly zooming to 100% either. It is a process.