That could work, but I don't think any developer is really wanting to go out on a limb and try.
With kids being encouraged to play outside and go to camp, teenagers partying and such, and adults being on holidays (or "vacations" for any Americans), it would be a risky time.
Of course there's always some exceptions to the rule, but in the winter seasons people are usually generally back in school/college/work and therefore have less free time so don't go out as much as they would do in the summer months, which means in the free time they have they'll just want to kick back in front of the TV with a game or something.
There's also the marketing of the Xmas season. When people are buying friends/relatives a video game for an xmas present, chances are they're going to buy one that's a recent release as the most marketing time a game gets is straight after launch, and if someone has recently seen an advertisement for a game that looks good, it will most likely stick in their mind and therefore be the most obvious choice. On top of the recent adverts there's likely to be hype from fans with all the "ooo have you tried that new game yet?" stuff.
Releasing a game in the summer months would be a good way to get purchases from a market of hardcore gamers who really play video games a lot, but it would not go so well for mass marketing based on these principles of marketing.