Now, admittedly Vick hasn't been proven guilty of the charges, and that is probably why he has not been dropped from the NFL altogether, but my understanding of the case is that it is fairly clear cut; it is not that he might have been involved, it is that he was involved. All arguments about slipperly slopes and innocent until proven guilty aside, this guy deserves the treatment he is getting.
I am sure his Nike sponsorship deal says something about being a role model and not bringing the brand into disrepute, and Nike have printed t-shirts with Vick's face and the word 'Hero' on them (prior to this incident) implying they expect Vick to be a hero. Nike themselves have said they do not condone animal cruelty (whether that is actually true is a whole other issue), meaning they do not consider dogfighting heroic, or a good role model. By involving himself in dogfighting, I would contend that Vick must have known he was taking risks with his career by engaging in this behaviour, and he did it anyway.
Now, I hope that Vick is going to be locked up for a long damn time for what he has done (and I hope that other asshole doesn't get to plea his way out of jail time), but I also think that what is happening to Vick now is something important. It seems to me anyone who would do something like this to an animal must have some status issues, and by stripping Vick of status, the punishment is fitting the crime.
As to the nutters who want to make this a race issue, or to dither about whether dogfighting is worse than rape (frankly, given that animal abusers are often people abusers, we shouldn't be splitting hairs, and I personally believe that animal cruelty is just as bad as rape), they need to stop framing this in terms of their favourite political issues, and think about what happened here: This guy did awful things to any number of animals, for which he should rot in jail at a minimum, and hell at best.