Same with me for Prey.
I can finally get rid of that fucking copy of Perfect Dark Zero that's besmirched my games collection for so long.
I have an answer. This promotion is not working yet. It IS active, their systems just aren't working right. An email went out earlier today to all stores telling them to override trade ins with the extra $10 until its fixed.
Why didn't this work when I tried it this morning?
I ended up trading the stuff in towards the Street Fighter IV game to get the benefit of the 30% (with edge), but this deal did not work.
Also update in TIV for OP: Transformers is now $5.