The US economy, and to a lesser degree Europe and Japan, regardless of debt levels are fortunate that they remain the R&D / high-end manufacturing centers of the world. Germany today still remains the largest exporter (exceeding China - check the last page of the Economist). This builds in a resilience which other countries relying on commodity based exports don't have. The ME maybe cash rich, but what are they going to do when the oil runs out?
We are witnessing tough times, but the fact is the developing world STILL relies on exports to US and European markets (the former in particular). This is a strong testament to their continued spending power. Yes these countries are in dept, but I ain't seen many going cap in hand to the World Bank or on the receiving end of international aid to prop up their failing economies. We've been here before in the 1930's, and no doubt due to the cyclic nature of things, we will end up here again in 20 years time.