Quote (atilla @ 17 Oct 2013 10:44)
no and life ends after highschool
This is true.
Anyways, at the OP question: Unless it's stated they have no parents due to them being killed or something, they have parents somewhere. They just have no importance to the anime in any sense. If they added in parents to every anime, it could waste time trying to develop them in some way compared to using that time to develop a character that is actually important to the plot.