I don't know if this is often the case but I did find this to be true in one case. The Special Offers wall SB value was not the same as the value from clicking a "snag it" button prior to having enough points. You click "snag it" and they say something along the lines of, "you don't have enough SB. Click one of the following offers to earn X number of SB." It wasn't a huge difference but it was more points through the "snag it" button. I clicked around and one time they offered me 6 more SB. Another time said to make me reach my goal they would bump it up to an additional 4 (so basically 10 more points than it was worth on the Special Offers home page).