Why do you think some deals sites are posting deals exclusively to facebook?
A certain bargain site (not woot) has a really good deal they've got going on that they're running through facebook. Of course, therein lies the problem: It's through facebook. As according to The Book of Rules 2:2, "Thou shalt not post bargains which involve the Book of Faces."
Do you think some sites are doing this so they can keep the deals from going viral through deals.woot, or do you think their move has more to do with more access to more information from their visitors?