I think that it is important to remember that they are human as well, and capable of shortcomings. But you should be understanding of imperfections, as you would hope someone to be understanding of yours.
I don't think that divorce is the most important aspect of determining whether or not you respect someone.
In most cases, reverence for parents promotes a healthy, mutualistic relationship. In some cases, such as when parents are heavily abusive, a lack of reverence for the parents can be to the benefit of the child who may leave his/her parents for a better life.
All-in-all, revering parents isn't always necessarily, but it's most often a good idea, as long as you don't hold your parents to be infallible.