The existence of MSP has always been a controversial issue. It's still viable through Windows 8 but default charges are in actual currency. Will they cease to exist within a year?
The system of 'fun money' was introduced at the inception of the Xbox Live Marketplace. For years consumers have complained how the system effectively encourages 'over charging'.
Microsoft seems to be finally wising up to the fact that their MSP blocks just won't fly anymore, especially with the PC community who have so many other choices available. When Xbox Live launched the Games on Demand service it didn't charge Microsoft Points. Many thought the rest of XBL would follow suit shortly after but it didn't.
They have argued in the past that currency exchange rates make using real currency a problem, while Microsoft Points were 'fairer' by comparison. Of course this is a false argument given that the actual purchase of Microsoft Points requires actual currency, which is of course tied to those very same exchange rates.