While the games are cheap enough here at their normal selling price (yay! for recovering exchange rate!). I can see where pkt-zer0's point is going. We're not saying it should be cheaper, but rather the deal is good enough as is.
For me though: These deals bring in the 'Shiney Things' factor. It's highlighted and mentioned on the main page, and makes me want to get it. The $1 off helps this as well, but is not a big deciding factor.
Review contests and other competing promotions would sound better, as this is a loss of the total of one or two games, rather that the total discount of everyone buying the promotion. Note: my economics skills are, well, nearly non-existent really, and I know there is more in play here.
(In these games case, I have two copies on CD already, else it would be a given)

aye, I won't have the money for it during the sale. :(

I tried a bit of the demo and it made me feel weird. I want to love it cause people keep raving about it. Why wont you love me love youuu

You don't have to love it. In fact, you don't even have to play or buy it. The bottom line is games are entertainment.
However if you fancy yourself a games expert, or wish to be knowledgable in the history of the subject, or especially if you strive to design them yourself, then you absolutely must experience this game in action. The demo is decent enough as far as it goes, but it only gives you the barest taste of how the full game mechanics play out. Some spells acquired later in the game (and the mere fact that you can pick and choose what missions you take) completely change the gameplay. Sacrifice is not a classic for superb implementation or dramatic storyline (though both are adequate or better) it is a classic because it is unique in its core dynamics. Definitely one to play, and this little deal makes the purchase special too. :) Now, if only I could decide whether I want G:CK or not. :/

You do, for exactly the same reasons as Sacrifice. Add to that a zany humor that'll bring tears to your eyes if you aren't squeamish, and you have a winner.

GCK was on my list for the last little while but kept getting pushed back for other purchases. Problem solved.
Though I believe that I would have bought both anyway, at some point, there is no time like the present. GOG sale +1 (or is it +2)

I'd like to introduce the word "art" somewhere in this equation

I would've taken advantage of this deal if only I hadn't bought both games a few months back.
Then again, it's only a couple of dollars extra, and GOG deserves it.

Indeed. Both Sacrifice and G:CK ooze creativity, something increasingly rare in modern games.

That's what I was aiming at in most of the rest of the post. I can't speak for G:CK yet, of course, but I'll pick it up shortly.