By recognizing that Casual/Hardcore are simply 2 points on a spectrum. The fact that people disagree exactly where on the spectrum those points exist doesn't change the fact that spectrum exists. So as long as they are designing content for people across the spectrum, it doesn't matter how you define the term "casual". It will be covered.
WoW already does this by offering almost all content in various difficulty levels designed to cater for different parts of that spectrum. So I don't really understand what the fuss is about.