Yes this is the right answer. The fare difference is due to the food served during the journey. Dont make it a issue.
you can check this for 2005 NDLS KLK Shatabdi Exp (Fare is 450 for CC)
but for 2006 KLK NDLS Shatabdi Exp ( Fare is 465 for CC )
also check for
2012...
more... KLK NDLS Shatabdi Exp ( Fare is 535 for CC)
2011 NDLS KLK Shatabdi Exp ( Fare is 465 for CC)
Here you can see the diff while the trains are running on same route, earlier Me, Mr Hetul & Mr Murli Discussed on this issue. Actually Mr Hetul Booked a ticket for one passenger for 2005 & 2006 and he noticed the difference. He asked me and I asked the answer Mr Murli then we decided to mail the matter to IRCTC and we get the answer mail from irctc that this difference is due to the food cost served in trains. In night train you will get the dinner also and it costs higher.
I think now the whole picture is clear to every one.
further discussion welcome on the issue.
Regards :)