You seem to have forgotten your own category : the ones who plays for a visual style. (I'm myself one of them)
Choosing a class on what they wear/use is not in the domain of mechanics, and neither in the domain of role/specs.
I think that in SWTOR we can add another category that doesn't exist in other MMOs : the ones who plays for an image/story.
Visual style will not make you win in pvp or do great in pve. That's more having to do with role playing than with game mechanics. I suspect only people playing a dps jugg/guardian will be people who like the 2 hander style, but those people will a minority and most people will probably jump ship if they only want to play a dps spec.