I blame the fact that we lost all 3 tosses, which put us on the back foot in every game.
If we had won the toss then I have no doubt we would have retained the urn!

(I may be clutching at straws!)
Tossing - a recent survey
In the summer 2013 tests, England won 3 tosses which they went on to win and lost 2 tosses which they went on to draw.
In 2010-2011, England won 3 tosses, winning, drawing and losing once, while Aus won 2 tosses which they lost
In 2009, England won 4 tosses, winning twice, drawing once and losing once, while Aus won 1 toss which they drew
In 2006-7 England won 3 tosses and lost 2 tosses. They lost every game.
In 2005 England won 3 tosses, winning once and drawing twice, while Aus won 2 tosses, winning once and losing once
Add to these the current series of 3 toss wins and 3 test wins to Aus and we get over the past 6 series:
England : win 16 tosses, winning 7 times, drawing 3 times and losing 6 times
Australia : win 12 tosses, winning 6 times, drawing 3 times and losing 3 times
So overall, England are slightly better at tossing (16/28) and if you do win the toss, you're more likely to come first (13win/6draw/9lose).
We also see that Aus are better at converting a won toss to a victory than England are, which perhaps means that England's recent successes are related to their adeptness at the toss. However, if we remove the current series (and just accept England are currently a team who've shot their bolt and Cook is leading a half-baked team), then actually while England would have an even better tossing record, there would be a very weak link between toss winning and game winning (10win/6draw/9lose). Which goes to show, none of the analysis above is that significant ;-)
Anyway, hopefully England will find their rhythm in the New Year and achieve better outcomes.