I don't see how some can't just get to the point that Blake and Bruce have something very much in common that is rare: they witnessed one or both of their parents being gunned down. Knowing that feeling and seeing that in Wayne isn't stupid at all, imo.
What's contrived is him being the only orphan to "connect" to Bruce in a place full of orphans, and with this being Gotham, I'm sure a sizable sample of them had their parents forcefully taken from them as well. So why was he the one to connect above everyone else? Because he is a character in the movie? That is lazy writing.
"If you want to save yourself the ticket price, go into the kitchen, cue up a male choir singing the music of hell, and get a kid to start banging pots and pans together. Then close your eyes and use your imagination." - Roger Ebert on Revenge of the Fallen.