I imagine because cold weather in places game devs traditionally care about (if you are not Japan, the US, Canada or one of the multi5 countries in Europe nobody traditionally cares), back to school and Christmas (plus I guess Halloween and Thanksgiving in the US and possibly something else in there somewhere for other places -- most places have a festival around that time of year) saw a spike there many years ago when games were more niche, considerably more of a luxury (especially if your market was primarily kids with questionable amounts of disposable income) and people still look to that for what are probably now all the wrong reasons (traditions are hard to break).
Things are spreading out decently nowadays -- I saw a bit of it during the GBA but on the 360 until today devs are consistently putting out really good stuff as late as early-mid March rather than just junk they need to go with a film or something. You might not win Christmas, especially not if some big dev comes in and drops a new adventure game/popular shooting franchise of the moment/popular sports franchise of the moment/popular driving game of the moment/popular one day to be longed for gameplay style of the moment*, but you can win their Christmas money. Prior to all that things went backwards as well. Between E3 and things announced at E3 being released there was often a fairly long wait. Today it is far shorter before big things start dropping.
*shmups, space games, point and clicks... I am sure we can all fill in the list of what once were mega popular games but now are somewhat niche.
With this said I am going to have to go look how it played out before the world more or less unified on this sort of thing. Back when Europe, North America and Japan were all more or less doing their own thing I am not sure it was quite like that. Being toys you would still get a bit of a Christmas glut but as far as the C64 and Amiga went then between what I recall and what my magazines said it was not quite as stark.
As for updates... Because developers also take up vacation during that time, I would think
Games... Probably because debs wait for the largest possible crowd. The timing of release is not a small factor in sales, so few dvd are willing to risk the game flopping purely because their audience was on vacation
Going by various things over the years then I would say no. Translators say northern hemisphere summer is the craziest time for them, while some devs seem to think permanent crunch time is a good plan the rest tend to save it for the run up to release (which if it is going to be September...).
I think lots of people shop during the fall and are willing to buy things more during this time. I do wish they'd space things out a bit more through the summer, though. It always feels like such a boring time of year for games. October is especially terrifying this year, in terms of just how many good games are releasing that month.