Okay, after class I went back to the store, and I asked the employee where the GTAIV ad went. He said they removed it because it indeed wasn't official art. He brought it out to me and upon closer inspection I saw it was just a composite of past GTA characters with a GTAIV logo overlayed on them. I didn't notice this before because I saw it just in passing and like I said I have been out of the scene so I didn't think to stop and stare at it. It's too bad it wasn't real but at least it built up more antipation to see the actual boxart for me.
Anyway sorry for the false alarm, I hope I didn't upset anyone. I'm actually disappointed though.