Remember they've been working on this back since 2007/8 almost as soon as they stopped supporting TDU1 with updates and DLC. They've had loads of time and are no doubt just bug-fixing and working on Q&A and distributions and preparing for marketing. Remember in a few E3 videos we saw collision bugs and the odd dropped frame so they still had a little bit of work to do. If they did indeed delay the game to acquire more car licenses and to model them then that would also account for the delay. And of course don't forget how crucial the netcode is for this type of game; it's not easy to test behind closed doors. Considering they said there is only one server per platform they had better be good ones.
If you're got WMD forum access you can learn a few things this year about game development timelines. They're planning for a November release and to pull it off they're expecting the game to be feature-complete by as early as April. That's a lot of months in between just for testing, polishing, optimising, getting certified by MS and Sony, and so on.
I'm thinking we might see release around May/June.