I think if it was entirely up to Microsoft, they would keep the points systems because it lends to more impulse purchases. It's been shown in numerous studies. In fact, impulse buying is one of the reasons why credit cards were invented.
Yes, it's easy to convert points to money in your head but it doesn't hit you the same as pulling out your CC. There have been many times I went all the way to the billing page of a purchase order, only to realize I didn't need it, changed my mind and put the card back into my wallet.
But with MS Points, there have been times where I bought it and then thought, man, I just spend $17.50 on a song pack for Dance Central...
Maybe this has to do with the rumors that hackers have figured out the algorithm on how to generate these codes and thus create counterfeit currency.
But I think it's perhaps more likely that since they are trying to tightly integrate the Xbox marketplace, Windows 8 marketplace, and Windows Phone marketplace, that they have to have consistency. Like in the tech demo where they had a customer buy a game for Windows Phone and it was playable on both the phone and the 360.
Also, by going with CC transactions, doesn't this shift the burden of fraud investigation to the credit industry rather than Microsoft?