If you consider principle repayment as savings increase, then paying off the principal on a credit card counts as savings. That's silly. If I buy a $1000 TV on a CC, then pay off the credit card, I haven't saved $1000.
I think counting debt repayment as savings is really just padding the numbers so people can feel better about their savings rates.
... as I said people can do what they want, but let's take these two example scenarios about a guy who makes $50,000 a year:
1) in January, I put $1,000 aside; In February, I buy a television for $1,000
2) In January, I buy a television for $1,000 on credit card; In February's CC bill I pay the $1,000 plus say $50 in interest.
So let's say it's now March 31st. Don't we agree that the difference between 1) and 2) is that in 2) you're poorer by $50 because of the interest - which is why you shouldn't borrow in the first place?
But my understanding of your point is that under scenario 1, my savings rate will be HIGHER by almost a full 2% (1,000 / 50,000, ignoring the interest for sake of example). That is because in scenario 2 I would have to count 1,000 as an expense twice.
I don't see how the guy in scenario 1) should delude himself in thinking he's saving that much more. He's saving interest which is great, but he's almost as "spendy".
Personally, counting principal repayment on my mortgage as savings does not make me feel better because it increases my savings rate; I'd just rather do the calculation correctly, and change my interpretation of the percentage to suit my circumstances, or dig into the numbers to properly understand what drives them.