If Canon start releasing camera based on Christmas I'll be damned. Xmas doesn't mean anything for most of the population of this planet.
Christmas is definitely something marketing types pay a lot of attention too. You are absolutely right about the demographics, but there will be a lot more sales of cameras based on Christmas than on the European Championship Soccer or even the Olympics. Yes, there will be a definite bias towards consumer models for the holiday, but I can't even imagine how many thousands of 5D cameras will be sold. Compared with how many pros will actually buy a new camera for the Olympics. (Note, I am not a religious person, but I have been in a BestBuy right before Christmas)
My personal opinion is that they will release 5dMKIII soon, because the 1D/Ds is not ready yet. The new 1 series has to be very high end based on what Sony just released(OLED viewfinder, High FPS, Actual AF in video, ETC...). Both for Video and Pro-sumer level. Sony is who Canon needs to lose sleep over, not Nikon.
Yeah, but is a 5-series camera really a typical stocking stuffer? It always seemed a weird time to aim for. They release everything so late in the year. Main wedding season is over in many of the more populated parts of the world, fall foliage season over, summer sports over, fall sports mostly over, summer trips to places to photograph over, etc. It just seems to me that they release them right as it enters one of the slower times for photography for a fairly large percentage of people in the world. Every cycle they release later and later, first they had them in stores by early sept then late then late oct then nov, so right when all the stuff many were hoping to use them for has ended, then they release them.