My friend, economic growth is not stagnant. Projections are based on current data but they do not cover uncertainties. For example; Chinese GDP may be growing at 10% in 2012. However, it may be growing 1% in 2020. This is how uncertain the economic future is.
Here is an example:
US have seen its highs and lows in its economic growth. Similar is the situation with many other nations.
Therefore, do not rely too much on projections. Fact is that US Industrial base is very powerful and it has remained strong for a long time. China has progressed a lot due to massive US Industrial investment in China. This investment have made Chinese populace tech-savy. And now you can see all the hooplah about China. But China still cannot develop every kind of product.
As far as India is concerned, it is far behind even China.
Therefore, US dominance is not going to be seriously challenged for a long term basis. Yes! We will witness rise of BRICS and world economic fibre will become lot less monopolized in the future. US may loose the title of sole-superpower but it will remain a leading WESTERN country and a powerhouse due to its immense resources and powerful Industrial base for many many years to come.
Wait till 2025 and we will see who is right.