The new XBL Microsoftpoints system that has been suggested by the users allows gamers to buy 400 points instead of 500 points (which makes sense if you only want 800 points) will be coming only to the US for now.
Microsoft said that “We are offering Microsoft Points in increments of 400 on Xbox LIVE in the US only, and we have nothing further to announce at this time. We’re always listening to the Xbox LIVE community for feedback and looking at ways to evolve Xbox LIVE.”
I think it will arrive to Europe eventually, but for now, only US residents can buy 400 MS points.