"It's President Obama's first international outing having won the election. It's at a time where the global economy is faltering a little."
The signs of another slowdown in Europe would worry the president as he faced the "fiscal cliff" - legislated tax increases and spending cuts that could push the US back into recession - at the end of the year, as would China's much lower growth this year.
"It's a really important time to take the temperature of the Asian leaders and for Asia to reaffirm itself as the great engine of the world," Mr Key said. The last time he met Mr Obama was at the nuclear security summit in South Korea in March.
Mr Obama missed the last big summit in the region, Apec in Vladivostok in September, because of the elections at home.
His officials are making much of the fact that his first visit since his re-election this month is to the Asia Pacific region.
Mr Obama visited Thailand yesterday and is to make a flying visit to Burma today to meet President Thein Sein and Opposition leader Aung San Suu Kyi.
Mr Key will follow suit on Wednesday.
Mr Obama will also meet former political prisoners who have been released as part of democratic reforms, but his Deputy National Security Adviser, Ben Rhodes, told reporters last week the visit was not a "victory celebration".
"This is a moment when we believe the Burmese leaders have put their feet on the right path and that it's critical to us that we not miss a moment to influence to keep going," Mr Rhodes said.
"It's an uphill climb and we want to make progress irreversible."
Mr Obama will arrive in Cambodia this afternoon and meet the leaders of the 10 countries of Asean (Association of Southeast Asian Nations) in Phnom Penh before it expands to accommodate the wider membership of the East Asia Summit at the dinner and a plenary session tomorrow.
This summit is gearing up to be more important not only because of the guest list, which will include outgoing Chinese Premier Wen Jiabao.
Tomorrow will be the start of a big new regional trade negotiation, the Regional Comprehensive Economic Partnership, which will include New Zealand.
It does not include the United States or Russia.
Former Labour Prime Minister Helen Clark attended three East Asia Summit meetings in three years from 2005. Mr Key has attended only one of the past three.
He got as far as Bangkok airport in 2009 before the conference at Pattaya was cancelled because of protests. He attended the 2010 summit in Hanoi, but sent Foreign Minister Murray McCully to Bali last year because it was held the week before the election.
