He did "technically" drop the belt. When he beat Cena at SummerSlam, he was beaten as fair (well as fair as a MITB cash-in can be) and square by Del Rio.
It doesn't seem to me that he's been champ since July, because he hardly appeared as the WWE Champ during that month long reign because of the storyline. I like his reign, not bored with it yet because I don't think there's anyone he should drop it to at the moment except for Jericho but if he were to keep it throughout the Jericho feud, I wouldn't mind. I like long title reigns, makes it more special when the guy finally does drop the belt.