I'm guessing Adventure Comics is not apart of the new 52 because it was originally used as the launching pad for Connor's ongoing as well as featuring the Legion of Superheroes. Both got their own books and of course now we're getting a "new" Superboy so they probably thought Adventure Comics was no longer needed.
I keep seeing fans state they think the books will revert back to their original numbering in a few months? Why think this? DC has pretty much staked the entirety of this relaunch on the basis of renumbering the two big books. DiDio has stated multiple times that was one of the things they decided to go all in on. I can't see therm refringe on that unless sales are down or a back lash happens.