Sure, Dow Chemical in theory holds the trademark for the word "Styrofoam", but the fact is that the word has become genericized. The public uses this word to refer to all forms of polystyrene foam. "Real styrofoam" is any polystyrene foam, not just the Dow product.
When everyone uses a word a certain way, it's not "wrong". Sure, people use the word in a way that a big corporation doesn't like, but that doesn't mean everyone else is wrong, it means the corporation is wrong. In this case, it means Dow's trademark on the word is now invalid, and indefensible. I have no idea why the Washington Post is such a corporate toady, helping Dow with their efforts to defend their trademark.
I like corporations. I believe trademarks are valuable. This blogpost isn't about how corporations are evil, but how journalists are idiots.