$18 on Frictional Games Store and only $16 on STEAM

[Temar]

We have had as low as 50% discount on Amnesia in our store. We do not set the price for the discount in other stores and did not know Steam would go for 20%.

That is interesting - why is Steam allowed to set any discount they want? Do they buy game copies in advance like a retail store? I always thought Steam would just offer a sales plattform like ebay.

Can you elaborate on that? I'm curious on how this works.