They usually release a patch on the day of release with minor changes such as the Liverpool takeover. The December one fixes most bugs that have come up in the game and it gives SI or us enough time to find out what bugs occur because someone might find one in the match engine and exploit it, things like this require fixing and can be fixed in the December patch.
What do you mean no time? The current version of the game will not have changed since the game went gold. So they could have been working on the release patch for 2 or 3 weeks. I know it won't focus on bug fixing, but you would think SI would want to fix any major issues ASAP rather than waiting until December.
The press release version has been out for a little while, but imo thats not enough people playing a game to identify all the bugs.
I class a bug as an annoying feature/fault that doesn't really affect the overall gameplay that much and so can be fixed en masse in december with all the other possible bugs that get identified over the coming weeks. Whereas a gamebreaker like FM 2010 crash dumps made the game unplayable and an emergency patch was released to fix it outisde of normal patching operations for SI.
Yes there isn't anything game breaking like there was on unpatched FM10... God that was bad... But a big company like SI would have a whole section team of people dedicated to QA though.