Ummm, let me clear some shit up right now.

The PSAT asks the religion question not for survey purposes, but to help you in a way to find religious based colleges and scholarships. Many branches of Christianity, and other branches of religion, offer scholarships and there are plenty of faith based colleges in the US. It's a way to help the student feel connected better to the college or to their faith

As for the whole thing on "Why is it the one true faith" well the OP is at a bit of a loss considering the fact that every religion on the planet has different secs and branches. (Hell, even Paganism) So, I think she is just picking on one faith in particular. In fact, would she ask that question if she saw the different Buddhist branches or sects? Zen, Theravada, Pure Land, Mahayana?

The fact of the matter is, and I say this as a religious studies student, we here in the west tend to group the minor faith branches together under general umbrella terms like "Islam," "Hinduism," etc, because living in a predominantly Christian nation with hundreds of branches existing, you tend to talk more about the Christian branches then you do the other religions. If you go into other countries with more Hindus or Buddhists, it would be a focus on the branches of their predominant religion and more umbrella terms for the minority. It's geography and local culture, not systematic oppression.

Sorry for the long post…it's ignorance like this that gets me a little tufted….