They are pointing out that Valve can actually afford to make the cube affordable while still making money if they wanted to.
They could, but since its literally just a PC it would just be subsidising PCs for something they likely aren't gonna make their money back, unlike XBOX or PlayStation, which are locked down and you are forced to use their store where they make the money back.
Will they make some of the subsidisation back? Sure, there will be some gamers that will be able to buy it just from pure numbers, but I feel like a massive chunk would just end up as office PCs with Windows on them in some office if subsidised.
The deck might make more sense to subsidise, but to do it for the gabecube doesn't make sense in the world we live in.