I don't care in anyway to which you care to keep your library, again I own both. However, I understand what digital means. As for the "CREDIT" portion, you're right it's credit. Microsoft isn't magically draining a bank account to give you the credit, it's simply a number on their marketplace with virtually no value to a company as large.
I'm trying to find a way to explain this better from my perspective, alas I'm not a smart man.
Hmm.. So, let me try it this way. Consumer A is impulsive, grabbing things on a whim digitally due to convenience of the way to shop. So, let's say Consumer A buys on average 5 digital AAA games a year at 60 dollars a pop. Now, this program suddenly kicks in. Consumer A sees this is a benefit to him, increasing his purchasing power. In the back of his mind, he's winning. This mentality enables his impulsiveness even more, now with the precendent he gets something for nothing, he'll buy more and therefore ends up buying 7-8 titles a year. Microsoft has now gained not only the same, but more profit from Consumer A.
What I'm trying to get at here is that we're exchanging nothing, for something to get more nothing. I would rather buy my digital game and know that, hey, this is mine and will always be mine. This was my choice, regardless of if it was available otherwise or not. I own more digital AAA, AA, etc.. games that were 60 bucks than physical at this point. However, I would never sell them back for a fraction, I'm not going to allow myself to be undersold at the grip of a company, regardless if I use it or not. I know it'll enable me to have more "buying power," when in reality I don't.
I also don't sell my physical games either, with few exceptions. This probably doesn't help explain my point any better, but what I'm trying to say is, it's making Microsoft more evil, not more generous.