That price applies to the base version of the device, which has 32GB of storage capacity (and about 15GB of free space out of the box, if one accounts for the operating system). You're still asked to pony up another $100 for the 64GB version of the device, but now, that now means paying just $449.
The 64GB Surface RT previously sold for $599. The 32GB version was priced at $499.
As Geoff pointed out last week, the Surface RT was a tough sell at those prices. The tablet's display resolution pales in comparison to the iPad's, and the Windows RT operating system is hamstrung by its lack of support for x86 apps and its somewhat unimpressive app selection. Also, Windows 8 tablets with Intel Atom processors have become dirt-cheap. Asus' 10.1" VivoTab Smart, for example, costs $399.99 at Amazon.
Now, at least, the Surface RT undercuts those Win8 offerings. It's just too bad it took so long. I can't help but think that, if the Surface RT had been priced more aggressively from the get go, Windows RT wouldn't have encountered such indifference from users and developers.