Sony has already nailed down their release date. It's set in stone. Sony fans have November 15th to look forward to, and finally get their hands on a next-gen console. Microsoft, however, wasn't so quick with locking down a release date. While many speculated that Gamescom would have been the perfect venue to announce it, Microsoft has decided, that it's not quite ready to unveil their release dates yet.
Thanks to a source working at Walmart, and Kotaku, we might now have a slightly better idea of when the Xbox One hits store shelves. This particular document shows a bunch of AAA releases which all are tied to Midnight releases at Walmart. And it looks like the Xbox One is listed just a week before the PlayStation 4, which for Microsoft would be an extremely smart move.
It is worth mentioning though that the document doesn't show a Confirmed status next to the Xbox One, which could just mean that it is Walmart's tentative date, and haven't actually been given any information from Microsoft.