It shows that the downturn was not as deep in the US as the other two centers. The economies generally bottomed in sync, but the US recovery has been so much more pronounced. Although a couple million fewer people are employed, US output has never been greater.
The UK economy has generally stagnated in recent years, which makes talk of a double or triple dip in the economy nonsensical. There was only one dip, from which it has yet to fully recover.
A more compelling case can be made for a double dip in the euro area. The recovery near mid-2009 ran-out of steam and it has been contracting anew for the better part of two years. Although its path has been different, and policies have been different, and the UK has its own currency, they have arrived at the same place: GDP 3-4% below the pre-crisis peak.