What I think gives Forcier an advantage over Threet and Beaver is that he's already an accurate passer. Henne's college accuracy was similar to his high school accuracy (best he did in HS was 64%, and his senior year was just under 60%). Mallett's accuracy was similar in high school to Henne's. Forcier was at 77% last year and is at 65% this year throwing more often, still better than Henne or Mallett managed in high school.
Forcier might not have a howitzer for an arm, but it's no noodle. He has to be the favorite to take over the job at some point next year.