Of course there has to be a reason for such a thing. No manager would want to be blamed for millions of outraged fans. So here's what an inside source had to say.
Quoted directly from Entertainment Weekly:
"The network wanted a chance to re-peat tonight’s return of Vampire Diaries and Nikita on Friday to give their midseason debuts some additional sampling. Diaries, in particular, is going up against Idol. Plus, there’s some local market pre-emptions that are going to mess with the scheduling of tonight’s shows in certain cities (Chicago and Baltimore, if you must know)."
Well, that's just great, isn't it. Well, I suggest we all grab another bowl of popcorn and pop in our Supernatural DVD's...again...while we wait seven more days for the long awaited return.