I take it you didn't read the link to how oral contraceptives work. They prevent ovulation, they prevent fertilization, and they prevent implantation.
Now, take Plan-B, it functions by preventing ovulation, preventing fertilization, and preventing implantation.
#1 So functionally how are they different?
#2 The FDA information specifically says that Plan-B does not terminate existing pregnancies. (http://www.accessdata.fda.gov/drugsa.../021998lbl.pdf)
#3 If it is the implantation issue, then why does Hobby Lobby provide low dose oral contraceptives that can prevent implantation?