While the article mentions "bisexual erasure" I think a problem as far as portraying bisexuals in TV or other media is "bisexual invisibility", caused mainly by the assumption that a person can only be straight or gay or lesbian, and that whoevever they're with or attracted to at a particular moment defines their orientation. It's easy, and sometimes not wrong, to judge a person's sexual orientation based on who they're sleeping with or married to.
I'm glad the article focuses on, among others, Callie Torres from Grey's Anatomy, because I know quite a few people who have said, "she's gay now," as though there's no such thing as bisexuality, and as though sexual orientation is a choice. It's funny. I'd think people who believe sexual orientation is a choice would be more likely to believe in bisexuality, but more often the opposite seems to be true.