Before you're given your walking papers (if it comes to that) you're referred to the proper channels for repentance. Its not as if BYU is trying to pass final judgement.

BYU is not enforcing repentance for salvation(although it is a natural by-product if done properly).
BYU is enforcing standards to instill a specific culture and lifestyle among its students conducive to the education the school is seeking to provide.

BYU officials believe that if every student lives up to or tries his/her best to live up to those standards, even those in the bedroom, that it will create a better environment for education. Its part of the BYU education.