Yah, the point was that the LA DA (who is an elected official) wanted to appear tough on "celebrity" crime and went after her full barrel and it was easy pickins.
Murder cases are a bit trickier for the DA to try and it's embarassing when they lose, especially if they bungle a case as they did with OJ. Now while Baretta is still cooling his heels in jail, the DA is not assured a conviction. And again, DA's run for re-election periodically so don't underestimate the impact that has on what cases they choose to prosecute in court.
In Ryder's case, for first offenses (evidently charges had not been pressed before in whatever other incidents there may have been) usually such things do not go to court (at significant taxpayer expense BTW) and are resolved by treatment, probation, restitution, etc. But there was no political downside for insisting on pursuing felony charges against Ryder since no special interest groups would be out there protesting.
Not so long ago, Halle Berry did an injury hit and run but was charged with a misdemeanor and got probation. (Civil suit is pending.) Ryder does a raid on Saks (not unlike, if rumors are correct, other celeb clientel are known to do on Rodeo Drive but who never seem to get prosecuted in court) and is a convicted felon. The Asst DA who tried the case insists that they are treating it just as an ordinary shoplifting case, then holds a press conference and makes the rounds of the morning talk shows.
Sure she should pay for what she did, but no doubt political motivations were involved in the way the DA chose to handle the case.