The reason being is that as a DPS class such as Sniper, there is no real need to dual spec because it wouldn't make much difference.
However, for someone like a sorcerer, they can be a healer and a DPS. THis makes being a Sorc as good as having 2 characters whereas for my self I am DPS either way.
I think you should have to focus your points in one direction and be happy with it! Otherwise roll a second character.
Thoughts?