I have only watched random games of the QBs listed in this topic but based on that admittedly small sample size and following the fantasy and sports analyses of the players, I believe this is not an example of bias but reflective of two other factors:
First, Pennington is a QB, with admittedly limited athletic gifts.
Culpepper, Leftwich, Brooks and Vick to include him as another example, are tremendously gifted athletes who played QB. Culpepper and Leftwich are the size of, or larger than many linebackers, incredibly strong and fairly mobile. Brooks and Vick are incredibly fast and agile, Vicks being the epitome of an athlete.
However, success in football requires ability that incorporates leadership and skill, not just raw talent. Vick displayed leadership and skill, Culpepper somewhat, the others not from what I saw. Pennington, in contrast, is a team player and even when he was injured was seen rallying teammates on the sideline. I am sure the movie "Rudy" is on Pennington's shelf in the AV room.
Short passes and ball control are how games are won. The big play is exciting, but for day in and day out success, the boring five to fifteen yard plays are how it is done. People forget the value of moving the chains in the day of televised highlights. I think of Jeff Garcia as another Pennington type.
The issue of racism or other forms of bias surely exists as every human forms opinions and expectations based upon their upbringing and personal experience. Much of the NFL ownership is of the "good old boy" network. Yet, the business of the NFL and the goal of winning precludes bias from being the basis of personnel decisions. Character, yes. Ability, yes. Race, hopefully not.
People should note too, the emergence of the Hispanic superstars in the league. Garcia, Romo, Bulger and Losman are all noted to be Mexican-American according to wikipedia. I was not aware of Bulger or Losman's nationalities, and having learned that, I can't say it changes my opinion of any of them. The NFL is well integrated, with racial representations that vary considerably from the national population. I am glad that the sport, in addition to providing such wonderful entertainment, also provides opportunity to so many athletes, many of whom have come from very modest backgrounds. Thankfully, many of these athletes represent the league and are exceptional role models. Sadly, the media focuses on those whose character is suspect or corrupt.
Pennington left behind many supporters in the Jets, and it was stated in one news article that much of the team was angered at his release. I wish Pennington success, and hope Culpepper, Leftwich and Brooks all find opportunity to further develop and showcase their talents.