[fjtorres]

The Microsoft Points cards go on sale from time to time.
One advantage (for MS) is that the listed product prices (in points) can stay constant while the price of the points themselves can vary.
It is a low-overhead way of processing micro-transactions; good for the vendor.
The trick is making it good for a majority of consumers, too. For people without credit cards or concerned about system crackers it is a good thing.