From what I remember with other stores online in the past their stock is such that they can take a bit of a loss here and there when it comes to certain items because they're still making a killing on others.
For example, I remember when HitMeNow.com bought the remainder of stock from a gigantic distribution center for various media stores around the US after the distro went under. At first they were offering all of those products for around 25% off MSRP with super-cheap shipping, which was good enough for most people. Then, the titles started going for $10 a pop rather than $30. Keep in mind, all of these DVDs were new (CDs as well, albeit for much lower prices). It finally reached a point where they still had so much stock they were blowing out everything else for $5 for DVDs, less for the CDs.
And the best part? One of their PR people still said that that was as low as they could put the price while still making a good profit off of what they paid per DVD/CD in the buyout. End Result: Everyone was saving bundles on quality titles and the business was still making hefty profits even if it seemed like they were giving everything away.
Now, they probably are losing quite a bit on the 360's and other similarly priced consoles but they're probably more than making it up on other items that they're selling.