This is one of your best observations Soriku. I am going to take it a step further by combining yours, Avinash's, and my own thoughts.
This is just how I classify it.
Non-traditional are the new demographics entering the gaming market (like my brother's 60 something in-laws or female)
Casual gamers is a broad term that can mean mainstream or gamer-lite. They are usually from the 18-35 or under 18 demographic. These are the people who stick with Madden, Pokemon, Halo, Final Fantasy, Smash Brothers, Mario, etc.
Hardcore play the obscure stuff.
Why does this matter?
Well non-traditional gamers can be or can become casual or hardcore gamers. Some older gamers are picking up tradition puzzle games, RPGs, and platformers. My girlfriend plays Counterstrike (which is too hardcore for me... God she's so hot).
I would cite regulation, but I know you will simply ignore it.
