I very much like the choice and use of the word spellcaster. I wanted witches and really don't associate the word mage with them at all. I've been fascinated with stories of witches both in fiction and in history since I was young and have enjoyed many movies and books that predate Harry Potter type of witches. I'm not putting them down mind you. My kids loved those books (I began buying them as soon as the public book burnings began) and I enjoyed the movies but it's not what I see as a witch normally. I could associate those witches though with the word mage maybe.. because they use the word wizard - which I can associate with mage.
I think they've catered to a wider audience by using the word spellcaster... I guess they could have gone with something like magic user but it sounds bland and has no panche... spellcaster at least has a nice ring.
I just think they are trying to cater to a wider audience by using spell caster.. and in my opinion they've succeeded.