The European release was pushed back because of the incompetent US publisher (forgot to include serial keys). The game is available at retail here but we can't buy it on Steam for over a week.
If that's the case, that's unfortunate. THQ was the publisher for the USA for the original S.T.A.L.K.E.R. and it didn't even have copy protection. And came with a bonus disc! Most surprising purchase I've ever made. Bought it the same day as C&C 3, which was the complete opposite experience. DVD-check to this day. Sigh.
Did THQ's lack of copy protection make GSC Game World angry and decide to switch publishers for this release or something?