I think this can be answered a number of different ways, but it certainly is not to be a landing spot for the most privileged Mormon kids--and since GPA/ACT trends track closely with income, BYU has been becoming increasingly elite.

In our graduate school orientation (yes, I realize grad school and undergrad are two different things, but I still think this applies) in business school back in the late 90s, Elder Perry spoke to us. He asked us what the purpose of the Marriott school was. The answer in his words: "to train future stake presidents." And he said that the Church saw the Marriott school as a tool for church members all over the globe to come get that training. He said to expect more and more students from Africa, South America, and Asia get into the MBA and Accounting programs as the years go on.

Again, that was grad school, but I think it is analogous in that regard to undergrad.