Another difference to, is that many Democrats don't campaign upon moral/conservative values whereas Republicans do.
Although both parties do things that violate the law or are immoral, when a conservative Republican does it it is going to get more press because of the hipocracy. Even though he isn't a politician look at the Rush Limbaugh scandal a few years ago. For years he had espoused conservative views and railed against improprieties committed by Democrats, so when it was revealed that he was a drug abuser people will make a big deal about it because he is a hipocrit. On the other hand Barack Obama sold and abused drugs in his past but it is not as big a story because he isn't on a moral crusade.