The bottom line is this: the team needs to do its homework, and developing players picked in those late rounds regardless of position also requires a little luck (although that's debatable too-if a team does its homework, odds are they'll find players that fit in their system more often than not). The Pats did their homework, felt comfortable with a guy like Tom Brady, and it paid off in spades-also helps Brady that he was drafted by the Patriots instead of a team like the Jags or even Lions (as a Michigan guy, I'm extremely happy Brady wasn't drafted here). Even Rodney Peete worked pretty well for a few years in the league, and I'm fairly certain he was a late round pick (sorry, don't feel like looking when he was drafted up-but he was drafted by the Lions, go figure).
I'm not surprised it's a Bears GM that says that-they could probably draft film in the late rounds and not be able to develop it.