And even if they have an almost adopted type of situation with their final foster parents, those parents still shouldn't have to pay all the college costs. They may not have even had the children placed with them long enough to save for that.
I mentioned in another reply, in Florida we have programs that offer financial assistance to kids that age out and continue their education. I support the programs, but there are things that should be acknowledged like it resulting in foster kids not getting adopted that otherwise would as financial strategy, or kids going into foster care right before aging out to qualify for the program.