Yes but valve already has a monopoly on the PC gaming market. Usually companies sell things at a loss to attract you to them so you buy other things while you get the good deal.

In valve's case, we're already in the store buying their games. There's no reason for them to sell it at a loss, because it won't attract people to steam.

Theres nobody out there saying "wow I would be a PC gamer playing on steam if I had a steam specific controller."

Maybe that's the case for the steam machines and steam frame coming up, but I kinda doubt it.