Those are batch 1 miners, the ones that should have been shipped by the end of the month. So you're basically paying to get toward the top of the list. Most likely miners that got freed up by giving refunds.
Well I just typed up a long post about how the GH/$ ratio for an Antminer today is currently better than the GH/$ ratio of the Prospero X-1 shipped in a month and a half (boldly assuming no more delays), complete with numbers and everything, but these stupid error 502's keep screwing me over. anyway, ill let people do the calculations themselves, hint, Antminer is less, and you can get it shipped in a couple of days.