Just caught up in that most recent speculation - and I thought exactly the same thing (and wrote it down in my review in my blog the day after I watched the movie *lol*). Why should Blake make the connection, and nobody else? What's so special about him to see beyond everything in a way no one else does? That's actually one of my pet-peeves with this movie. If not show Blake as that blond boy (and I share the sentiment that he'd be to young), then why not mention some connection here that would have given Blake the final piece of the puzzle?
Given all the things that come out of the left field in this movie, Blake, Miranda's relationship with Bruce, Miranda getting power over Wayne Enterprises (why not Fox? Somehow must have missed something there), Catwoman's story that's more or less stand alone... and yes, the similarities to BB in terms of let's burn down Gotham City... And I won't even talk about Bruce's still mourning Rachel, his physical appearance at the beginning, the way his broken back just healed without further damage, and I don't quite know what to make of Alfred in this movie, either.
Somehow, it seemed to me as if TPTB tried to cram too many new details into that movie but somehow failed to actually put a new twist on it. I loved Bruce's story, and honestly, I'd have been perfectly happy if that had been the only focus of the movie.