Microsoft is apparently able to achieve such a low price by subsidizing the console through a two-year subscription.
The Verge tends to know what they’re talking about, so I’m willing to float this report, as it's a business model that makes sense.
The subscription would cost $15, and be paid out monthly. The bundle would also include Kinect, access to an Xbox Live Gold membership, and possibly other premium video services.
There would be a warranty covering the two years, and like other subsidization models, users could opt-out ahead of the two year mark by paying an early termination fee.
It’s a compelling idea. While I can’t tell you a source confirmed it to me, I’m inclined to believe it, even if we don't hear more until E3.