there are few things which I have said on PDF many times but there are always new people who raise the same question and then get confused with few basic things........
first, if you want to measure 'strength' of an economy, not its power to import, then you need its PPP value which adjust exchange rate. here we find GDP of India was $4.45tn in 2011 but its still manipulated by the US/UK since 2006. as, till 2005, we had a different way of measuring GDP on PPP which used to include 'estimated' 'undocumented' part of GDP also. and I remember, this way GDP of high population 'developing' countries was around 60% to 70% higher, of the country like Brazil/Turkey it was around 10% higher. and for the developed nations, the difference was hardly around 1% to 3%. like as below:
for 2005, India's GDP at PPP is estimated at $ 5.16 trillion or $ 3.19 trillion depending on whether the old or new conversion factor is used
It's official: India's a trillion-$ economy - Times Of India
means, GDP of India on PPP was already $5.16tn in 2005 and since then India registered around 9% growth on average for 2006, 2007, 2008 and then around 8% on average in 2009, 2010, 2010 period. (these British SHiiiTs were mainly behind all these manipulating of India's datas, I personally know this.........)
this way, if GDP of India was $4.45tn in 2011 by new method then it would be around
$7.5tn on PPP by 2011 if we consider the old method which was in application till 2005
also, its true that population of India is 1.2bil but 850mil people might have hardly $2.0tn share in it, leaving around $5.3tn for rest of 350mil Middle Class with per capita income of around $17,000 on PPP which is close to Very High HDI countries like Argentina, Poland etc. hence you may say, India has 850mil people with per capita income around $2,500 and rest 350mil population with $17,000 on PPP........
when you consider India, you would alway think that even if population of India may become 2.0bil one day, their 350mil middle class is more in number than US also, the so called 'strongest' in your list, with projected growth rate over 7% for next 20 years, the minimum