Apparently it doesn't apply to all games just some.
Yet when you check out it doesn't tell you WHICH games.
So you have to add to the list, and "Try" and check out. If you get to the window where you can actually purchase it (past the greeting message etc) I'm guessing that means you can buy it.
And if you get the message you have to remove it from the cart and try with other stuff. Kinda hassle but better than trying to cross check it all with GOG.
Oh and apparently steam doesn't like that.
"It looks like you've been attempting a lot of purchases in the last few hours. Please wait a while before trying again."
bullshit. Adding a game, trying to check out, being told to F off because of "prices differences" is NOT "attempt a lot of purchases". It's mean trying to figure out WTF I can actually buy.