Also puzzled about this too, since the pricing scheme differs from a per/usage AWS fee. Maybe they're going the way of traditional shared hosting companies by banking on a very small percentage of their users actually ever achieving high traffic?
You only get the advertised rate if you pay the full year in advance. This allows them to advertise a "monthly" rate that is actually "$holycow/12" while also advertising "no commitments!"
edit: and, at 613M of RAM ... I'm not sure exactly what someone would plan to do with such an instance of Windows, but it won't be much.