The Raven- Legacy of a Master Thief apparently won't be removed since it's not featured on the sale.

Nordic and Frictional already explained. It's regionally priced. GOG agreed to have newer games such as The Raven, The Critter Chronicles, and A Machine for Pigs regionally priced in the traditional sense, in line with the pricing at other stores, which is fine by the publishers. But the one global price for the older games hinged on the excuse that it was literally one price in a specific currency. Once GOG started using multiple currencies and thus multiple actual prices, the publishers no longer have an excuse to allow GOG to undercut other stores.

I already knew that. I just wanted to point out not the entirety of the catalog will be gone.