It does. Aether is part of the world in its entirety. That Garleans have no ability to wield is of no matter.

As to the rest - it is quite simply a matter of genetics. While ability can and does vary within those populations who are capable of wielding magic, Garleans lack those same hereditary traits that allow for repeated, reliable, manipulation of aether.

[For the time being, he elects to not mention that his current form is Garlean in appearance. It's not truly necessary, at the moment.]