First, let me qualify my statements by saying I'm not a criminal lawyer, so I'm no expert. But with that said, regarding the prosecutors, people are over-reacting and trying to blame the prosecutor. if you want to blame someone, blame "the system."
Domestic dispute cases are regularly pled down, even with damning evidence. Do any of you know any cops? Talk to a beat cop and they'll tell you that they deal with domestic disputes on a daily basis. If you put everyone in jail for extended periods of time for domestic abuse, a big portion of this country would be behind bars, because that is how prevalent domestic abuse is (or even run of the mill physical arguments between couples). Court systems would be flooded, and jails would be overflowing even more than they are now.
Its like DUIs. Do you know why DUI related offenses (e.g., killing someone while driving drunk) are relatively punished lightly (e.g., Stallworth, Little). Because nearly every adult male has gotten behind the wheel after a few drinks, including judges, CEOs, lawyers, politicians, etc. If we had super heavy DUI offense penalties, again, a lot of folks would be behind bars. Policy and priorities play a large part in criminalizing certain conduct, penalties, etc. This is a male dominated culture, and thus the reason in part that domestic violence isn't aggressively pursued (and DUI related offenses). I'm not saying it is right or wrong. "It is what it is."
Though a different situation, look at Jim Irsay. This guy has a bunch of oxy in his car, $40K in cash, and he gets a slap on the wrist. If that is some inner city kid, or some tweaker from rural Washington, they'll probably throw the book at him (e.g., possession with intent to distribute). So money plays a part as well obviously, and then add race to equation and the system looks REALLY BAD.
Just my 2 cents..
EDIT: Regarding the video, I saw Rodney King get the crap knocked out of him, on video, and those cops got off on the first trial. So video evidence isn't the end all be all....