Although increase in average income will definitely mean that there has been overall increase in the total income of our country.
How ever, this cannot be used to conclude that there has been economic development in all sections.
Several areas may have suffered a detorioration in economy. Also some area may havn't developed at all, ie. ,may have remained stable.
While on the other hand, many other areas may have under gone tremendous development too.
The average income only shows the mean income of a person. In a country as varied and as diverse as India, that too with a population of 125 crores, increase in average income is surely not a very reliable data to state that all sections have got better income economy.