Had the Jets made Kellen Clemens the starter, they probably would have been comfortable with depending solely on the running game, special teams, and defense. Clemens would have been a game manager in every sense of the word. This probably isn't going to happen with Mark Sanchez. Sure, at the start of the season, the Jets won't lean on him too much, but the goal isn't just for Sanchez to avoid mistakes. It's to develop him into a franchise quarterback.
I doubt the Jets would have put a second thought to the passing game with Clemens. Now they need to think of giving Mark some weapons. So much of developing a young quarterback is putting him into a position to succeed. The two examples I always use are Ben Roethlisberger and David Carr. Roethlisberger had a great defense, a bruising running game, and a Plaxico Burress/Hines Ward tandem at receiver as a rookie. Carr had nothing surrounding him in Houston and pretty much had to do it all for himself as a rookie.
The Jets' situation looks closer to the Pittsburgh model than Houston except for at receiver. Add a Marshall to that mix, and things change very quickly. A Marshall-Cotchery starting duo would be one of the most productive in the league. You could see Chansi Stuckey in the slot, and David Clowney appear in spread sets to stretch the field.
You don't trade up to the fifth pick and guarantee $28 million to a quarterback to not give him weapons. Do the Jets now go out, make one final big splash, and land Brandon Marhshall?