The US has always benefitted from the relative stupidity of the rest of the world. If the choice is between investing in America or investing in Venezuela or Russia, the choice is pretty easy.
So, America has always attracted foreign investment because the alternatives are often unappetizing. They are today.
Where would you put your money today? In the Eurozone? In Brazil, Russia, India, or China (the BRIC countries)? The US is undoubtedly a country in relative decline, but even in decline, it looks like a safer haven for investment money that the available alternatives.
The combination of very slow growth and zero interest rates is perfectly consistent with a world that prefers to "park" it's money into the "relatively" safest spots on the planet. But, without investment ("animal spirits," Keynes would have said), economic growth will remain paltry.
Sooner or later, the realization will dawn that the prospects over the next century are much brighter in Asia than in the West and money flows will begin to head that way. That will require some changes in Asian laws and treatment of foreign capital and foreign ownership. But, that will come, in time.
In the meantime, the US will appear the least bad of some very bad alternatives.