Author seem to be not having knowledge about current population statistics.(atleast 2001 census). The SC/ST population together as on 2001 census is 25% of indian population. if you deduct from OBC % of 52(which u claim in ur article as per 1931 census) will come to 27%). But To my knoledge the 1921 or 1931 does specify these percentages separately. The TRUE fact is that in 1993 OBC list contains 1300 castes and is doubled to 2600+ in 13 years. Another fact is that at the time of classification of OBC after independance some castes which are poor in large percetages does not included because of their leaders who represented well in number. But they are now willing to join this OBC group.
The reservation on caste based is not good to the society. It should be based on economy and/or based or rural back ground based on distance to basic education and health facilities. Get rid of the caste perspective at all.
Rules : grace marks should be added as x% of total marks achieved by candidate Economy in anual income in Rs and levels
1:< 10K, 15% 2:< 20K, 12% 3: 20K - 40K, 6% 4: 40K - 60K, 4% 5: 60K to 150K 2% same should be done for rural people. rest u understand