I watched that game live and I very well remember the play's Henne made. Yes, there was the long bomb to Ted Ginn that we all remember, which also happened to be the one legitimate big play that Henne made in 14 games. Other than that, I saw Henne making accurate passes that really aren't big plays. Nice throws, but not big plays.
Big plays are different than making good passes. Either the QB connects a bomb (like in the Ginn pass), or when the pocket breaks down he gets outside it and finds a man way downfield and makes something happen. Also, there are the type of big plays like Roethelisberger to Holmes in the SB, where he finds a guy in the back of the end zone and gets the ball to him in the only space where both the defense couldn't get to it, but the receiver could and still get in bounds. Other big plays are Eli Manning in the Super Bowl somehow managing to wrangle out of the defender's grasp, get outside the pocket and get the ball to David Tyree.
A QB can throw nice intermediate passes all day, and that doesn't make him a big play QB. Henne does this very well when he is on, and I'm not going to deny him that. But these things are not big plays, and while some QB's are able to make the big plays and yet not hit intermediate ones consistently enough, like Sage Rosenfels, making them not great starting QB's, its also possible to hit the intermediate ones and not hit the big ones enough. You can be a much better QB than the guys who can make mostly big plays, even a very good QB, but a franchise passer has to be able to make both the intermediate plays and the occasional big play. That what separates him from other QB's, and gives him the edge to come out ahead nearly every Sunday.
Hitting one big play a season doesn't make you a big play QB. Chad Pennington completed more deep passes with worse receivers than Henne. We all remember the occasional deep balls to Ginn which happened more than just one occasion, yet he also got 38 20+ yard plays and 8 40+ yard plays in 16 games of 2008. Henne in just 25 less attempts in 2009 had only 23 20+ yard plays and 4 40+ yard plays.
We all know that Pennigton wasn't a big play QB, but it is absolutely ridiculous to suggest that Henne has been either. Ironically, the video showed Mark Sanchez showing the difference between himself and Henne, as he clearly made more big plays in that video. He has to get better at the little things to be a great QB, but big-play potential is there.