Well something came along as that is why the hashrate has been been going sky high for the last couple of months, private mining farms in China mostly seem to be the cause

Read over at the mining forum here, Spondoolies have been bringing out new machines and also Bitfury has machines which people are speculating is one of the causes.
From what i see, Bitfury is not selling these to home miners, mainly for using themselves, but as GM could potentially be quite a large buyer, it makes me wonder if Bitfury is also selling them these new machines and Spondoolies will only sell their miners now for really large orders so GM couod be getting these in too.

Also perhaps GM has opened up a new facility somewhere with even lower costs to set up and a good rate of electrricity so the combination of both of those things plus the newer miners means they can offer the lower prices.