Apologies in advance if all this is really obvious, but there seem to be a number of people on this thread that don't understand how a public company works.
Both Boeing and Airbus have financial years that line up with the calendar, and so anything you land before 2014-12-31T23:59Z (Airbus) or 2015-01-01T07:59-08:00 (Boeing) gets counted towards that year's results.
Why does that matter? Because: a) both are public companies, which the stockmarket judges by their annual results, and b) senior executives receive large percentages of their annual income based on achieving performance / stockmarket-related targets.
Therefore, both companies have a huge incentive to close deals by 31 December. As has been mentioned up-thread, this provides a hurry-up-and-go to both the vendor and the buyer, and games of brinkmanship are probably pretty common.
The only differences between the behaviour of the two companies appear to be:
1- Airbus's press conference is +/- 1 week later than Boeing's.
2- Airbus are more willing to hold
PR announcements for deals signed in late December until their press conference.