Fortunately, that's just not true. The 80% statistic is an enduring myth I see quoted frequently, but studies just don't back it up. The divorce rate seems to be about the same, whether a child is autistic or not. Even worse, the show quoted that the character's therapist told her that it was true. Lesson 1: Don't believe everything your therapist tells you! Lesson 2: Just because your child is autistic, doesn't mean you're doomed to divorce.
You can read an earlier discussion of this topic on my Divorce and Autismpost. Please don't skip the show because of one bad statistic. Autistic kids are varied, and every family is different, but in general, Parenthood seems to do a pretty good job of presenting the joys and struggles of raising an autistic child.