Quarterback depth charts are a difficult thing to evaluate. Do you err toward the team with the best No. 1 option or the team with the safest amount of protection behind him?
The safest way, I think, is to use a healthy combination of the two. A team with one Heisman candidate but no other viable players under center cannot be considered to have one of the best depth charts in America. Likewise, a team with two viable players but no viable starter is discredited in a similar way.
Thus, in order for a team to make this list, a combination of two things was needed: (1) a quarterback who can be trusted to compete for a conference championship and (2) a backup who can be trusted not to let the season implode if the starter gets injured.
Oregon, for example, fulfills category (1) with Marcus Mariota but not category (2) with Jeff Lockie, which is why it has been excluded. On the other hand, Michigan fulfills category (2) with either Devin Gardner or Shane Morris, but neither of those quarterbacks fulfill category (1).
There is definitely some wiggle room for argument, especially in regard to the teams with blue-chip starters.
I prefer certain young high-upside backups to others, but there are arguments to be made both ways, so feel free to chime in below and let me know where you disagree.