If one goes by the CPC Recommendations and Resolution and the subsequent Pay(Revised)Rules 2008, it appears quite clear that the erstwhile three Pay scales of (starting with pay of Rs.5000, 5500 6500) were merged into one Basic with Grade pay of 4200. This shows that the erstwhile Scale of pay with starting pay of Rs.4500 was left out intentionally. This being the case, apparantly, your friend has no case.
Therefore r, if your friend's department has not done anything to upgrade the post of erstwhile Scale of pay of 4500 to 5000 or higher (for the purpose of fixing pay under Revised Rules), then, I am afraid, the grade pay of 4600 has been correctly denied and only 4200 has been given.
(Modification) (added on 22.10.2009)
The error pointed out by the learned friend (herein below) is regretted. What I had in my mind was that the Grade pay had been correctly fixed at 2800 and not at 4200. (This is due to the fact that Pre rev scales of 5000,5500 and 6500 were only clubbed and 4500 was left out).
I thank lijijee. )