They don't know that, if they sell cheap enough it might be worth it for a random office somewhere to order a hundred and use them as work computers with no intention to ever buy a game in them. Also they aren't going to be locked, nothing prevents you from getting one and run games purchased in every market under the sun that isn't steam (and/or pirated games).

I don't think they have any certainty that they'll even make decent money on them. I am hopeful that this will be good for everyone but can't exactly see how at the moment.